Success in international Junior competition promises future success in pro tennis. Among youths winning Junior Slams in the 1970's and 80's were future multiple men's-Slam winners Borg, McEnroe, Lendl, Wilander, and Edberg. (Edberg won all four Junior Slams in 1983.)
 
But there are no guarantees, especially in more-recent times. Only six Junior Slams during the fifteen-year period 1995-2009 produced winners who later won men's Slams. Here listed are those winners of boys' Junior Slams during that period who as pros later became men's Slam champions.
 
Roger Federer, won Wimbledon Juniors 1998 at age 17. (Won first men's Slam at Wimbledon 2003.)
Andy Roddick, won Australian Juniors 2000 at age 17 and U.S. Open Juniors 2000 at age 18. (Won U.S. Open 2003.)
Stan Wawrinka, won Garros Juniors 2003 at age 18. (Won Australia 2014.)
Andy Murray, won U.S. Open Juniors 2004 at age 17. (Won first Slam at U.S. Open 2012.)
Marin Cilic, won Garros Juniors 2005 at age 16. (Won U.S. Open 2014.)
 
Of the sixty Junior Slams played during 1995-2009, 22 produced boys' champions who as adults later attained the world's top ten, and 37 produced boys' champs who later reached the world's top fifty. These results, accordingly, indicate probability that the winner of a given Junior Slam will later:
 
-- win a men's Slam = 10%
-- attain the men's world top ten = 37%
-- attain the men's world's top 50 = 62%
 
The process where a Junior champion eventually becomes a pro superstar at about age 24 is demanding to extreme degree, requiring years of commitment and high motivation. A typical path might see the rising aspirant even as a junior begin competing in the ITF Futures circuit and then in lower-level ATP pro Challenger events. He accumulates an official (rolling-12-month) world ranking, which must grow to achieve entry into the richer Challengers.
 
There are about 150 Challenger tournaments each year. Each event consists of a 32-place main draw preceded by a 32-player qualifying event, attracting recent veterans of higher-level play, regional stars, recent college players, and the young risers. The Challengers can be deemed the minor leagues of pro tennis, where on-court success opens the way for higher opportunity. A world ranking in the second hundred generally brings entry into the qualifying rounds of main-tour events. A rank in the first hundred usually brings direct entry into the main draws of Slams.
 
We now turn to today's population of young and rising pros who are now amid their journeys toward possible superstardom. We view them in three age cohorts, starting with the teenagers and finishing with the 23-and-unders, whose leaders are the ones now closest to the heights. Who are the leaders of the cohorts? Will they be able to stay ahead of their contemporaries as they approach the important age of 24?
 
TODAY'S TEENAGERS (19-AND-UNDER)
 
Each player's listed score is intended to represent his current playing ability, having been calculated from his playing results in the six-month period ending 28 February 2015.
 
Players 19-and-Under. Six-month ranking (Sep 14-Feb 15)
1. Borna Coric, age 18, height 6-1 (Croatia), score 13.8
2. Nick Kyrgios, 19, 6-4 (Australia), score 11.0
3. Thanasi Kokkinakis, 18, 6-5 (Australia), 7.6
4. Yoshihito Nishioka, 19, 5-7 (Japan), 7.1
 
Our current leader of the teenagers, Borna Coric, won the U.S. Open Juniors at 17 in 2013. Having earlier reached the semis in Australia and Garros Juniors and the quarters at Wimbledon, he became tops in that year's official junior rankings. He then showed good success in ITF Futures, winning five events. In late 2014 he won the ATP Challenger at Izmir 2014, penetrating the ATP's world top hundred. A prime win came in 2014 Davis Cup play over Jerzy Janowicz, helping Croatia defeat Poland 3-1. There was also a win indoors over an ill Nadal.
 
Coric's strong rise now placed him regularly against top-hundred opponents, and he achieved few wins in early 2015. But with a reputation for determination, and with support from Croatian legend Ivanisevic, Borna regained his upward momentum in main-tour action in Dubai in late February. In defeating an off-form Andy Murray before the world, Borna displayed relentless ground-stroking power and accuracy superior to Murray's on this date. (Borna was, however, swept aside by an on-form Federer in the tournament semis the next day.) Borna thus moved ahead of the earlier leader in our tally, Nick Kyrgios, who did not compete in February.
 
Nick Kyrgios won Australian Open Juniors in 2013 at the age of 17 without losing a set. Nick's brilliant transition out of the Juniors and into his successes in the three most recent men's Slams is of an order rarely seen.
 
His six-month score here largely stems from his reaching the Final Eight at men's Australian Open 2015, losing to eventual champ Murray, and his winning two main-draw matches at U.S. Open 2014. Nick also led in our tally of results by the identical cohort population in the preceding six-month period (March-August 2014), when he reached the Final Eight at Wimbledon.
 
Born in Canberra of Greek and Malaysian parentage, Nick's recent triumphs have come with intervening injury problems -- shoulder, arm, and back. But with a playing style reminiscent of Jo-Wilfried Tsonga and with an in-your-face manner suggestive of his early attraction to basketball, Nick's easy power and, athletic elasticity, combined with the impressive serving and attacking that he showed against the defenses of Andy Murray at Melbourne Park, all argue that his achievements are likely to grow.
 
Like Kyrgios and Coric, Thanasi Kokkinakis also was among the first four in our tally for the previous six-month period. Born in Adelaide of Greek immigrant parents. Thanasi had a fine career as a junior, at age 16 defeating Borna Coric in the semis at Australian Open Juniors 2013 before losing in the final to Nick Kyrgios. He later was finalist at U.S. Open Juniors 13, losing to Coric in split sets. He competed in Futures tournaments at early age, and in 2013-2014 he showed excellent results in Challengers and in qualifying rounds of main-tour tournaments, reaching world ranking of #150 the end of 2014. Main-tour successes in early 2015 included wins over Benneteau and Gulbis.
 
The only newcomer to the top four is Yoshihito Nishioka, a left-hander at listed weight 138 pounds. Yoshihito had moderate success in Challengers during the period, winning the Shanghai Challenger last September. In main-tour action, he defeated Borna Coric in the qualifiers at Vienna, and he recently advanced from the qualifiers to achieve his first two main-tour main-draw match wins at Delray Beach. He lost in the third round at Delray, outclassed in reach and power by Bernard Tomic.
 
One other male teenager requires note. Alex Zverev, at ninth place in our six-month scheme, is our highest-scoring 17-year-old. Born in Hamburg and tall at 6-6, this son of a former pro and younger brother of another was Garros Juniors finalist in 2013 and won Australian Open Juniors in 2014. He had good success in Challengers thereafter and reached the quarter-finals in main-tour action at German Open, played on clay in his city of birth.
 
Our four leaders in the cohort are well ahead of all others in the current teenaged cohort. We can expect that during 2015 the four will continue as rivals in upward movement, now mainly in main-tour action. The immediate edge seems that of Kyrgios, who will exit from the teenaged cohort when he turns 20 in late April. His injury difficulties seen during 2014 seem the only threat to his progress.
 
THE 21-AND-UNDERS
 
Our survey posits 24 as the most likely age for entering the world's first ten (recent examples Raonic and Nishikori), suggesting that the top performer among the current 21-and-unders is probably about 2-3 years away from reaching that milestone. Remarkably, the two youths atop the teenager list are also atop this cohort:
 
Players 21-and-Under. Six-month ranking (Sep 14-Feb 15)
1. Borna Coric, 18 (Croatia), score 13.8
2. Nick Kyrgios, age 19 (Australia), 11.0
3. Jiri Vesely, 21, 6-6 (Czech Republic), 10.9
4. Lucas Pouille, 20, 6-1 France), 9.9
5. Dominic Thiem, 21, 6-1 (Austria), 5.9
 
In third place behind the two teenagers is left-handed Jiri Vesely, a hard-hitting belter from Czech Republic, who also stood third in our measurement for the preceding six-month period, behind Jack Sock, who was subsequently sidelined with injury, and Dominic Thiem, shown in fifth place here. Vesely's wins in 2014 were mainly on the Challenger circuit, but he defeated Monfils at men's Wimbledon 2014 prior to a four-set loss to Kyrgios. He won his first main-tour tournament in Auckland in January 2015, where he emerged from the qualifiers to defeat five opponents, all in the world's first 70, with loss of only one set.
 
Lucas Pouille lost to Vesely in the qualifiers at Auckland but because of a withdrawal was then admitted to the main draw, where he managed to reach the semis. Earlier in the six-month period he advanced from the qualifiers to reach the final sixteen at Paris Indoors, scoring top-70 wins over Steve Johnson, Nieminen, Karlovic, and Fognini. Success also came to Dominic Thiem, who led the cohort during March-August 2014. His upward run continued at U.S. Open 2015 where he scored three main-draw wins against top-hundred opponents (Gulbis, F. Lopez). His climb then abruptly reversed, but his big serve and big forehand promise renewed success whether on clay or hard.
 
THE 23-AND-UNDERS
 
Here is our highest cohort -- the young risers most ready to enter the men's top ten:
 
Players 23-and-Under. Six-month ranking (Sep 14-Feb 15)
1. Grigor Dimitrov, age 23, height 6-3 (Bulgaria), score 25.5
2. Bernard Tomic, 22, 6-5 (Australia), 21.8
3. Borna Coric, 18 (Croatia),13.8
4. Nick Kyrgios, 19 (Australia), 11.0
5. Jiri Vesely, 21 (Czech Republic), 10.9
 
The early talent, athleticism, and power of Griigor Dimitrov produced triumphs at Junior Wimbledon and Junior U.S. Open 2008, attracting high predictions universally. He has already penetrated the world's first ten, and has been at the top of this cohort in both of the last two six-month periods, though his results have declined since U.S. Open 2014. They include a final-sixteen finish at Australian Open 2015, ending in a loss to Andy Murray in four close sets.
 
More unexpected was the second-place finish here of Bernard Tomic, who penetrated the world's first hundred in 2011 as a teenager whose softish sliced-and-diced game seemed incongruous in a player with Bernie's excellent height. With further growth Bernie acquired more powerful weapons, and now, when he chooses, he delivers full-power ground-strokes often and accurately. His father (also his coach) has at times fallen out with Australian officials over Bernie's management and was said to have threatened moving the family back to Europe. Bernie won the 2008 Junior Australian Open at age 15, the youngest age ever to win that event, and also U.S. Open Juniors 2009.
 
The gap seen here between the top two and all others aged 22 or 23 is worthy of note. Penetration of the cohort from younger players is also strong through several places beyond those shown here.
 
The agreement is hardly perfect, but the current picture among today's male young-riser cohorts tends to support the numerical probabilities facing junior aspirants given at the outset here. Grigor Dimitrov, leader of the 23-and-under cohort, penetrated the world's top ten at Wimbledon last year, then slipped just outside, returned, and is now again just outside. Second-place Tomic is inside the first fifty and on a strong upward run. Most impressive is the 21-and-under cohort, including the group who have already surpassed all 22 and 23-year-olds save Dimitrov and Tomic in our calculation. Of these, Vesely and Kyrgios are inside the world's fifty, Thiem as well, and Coric very close.
 
THE WOMEN -- TEENAGERS
 
The sacrifices and career patterns among the top female risers are similar. The women's ITF pro circuit takes the place of the men's Challengers as the foremost bridge to the main tour and Slams.
 
Players 19-and-Under. Six-month ranking (Sep 14-Feb 15)
1. Belinda Bencic, age 17, height 5-9 (Switzerland), score 14.0
2. Katerina Siniakova, 18, 5-9 (Czech Republic), 9.7
3. Oceane Dodin, 18, (France), 7.0
4. Elizaveta Kulichkova, 18, 5-9 (Russia), 6.8
5. Ana Konjuh, 17, 5-9 (Croatia), 5.5
 
Belinda Bencic has been a favored topic in this column ever since her double triumph at Junior Garros and Wimbledon 2013. Since then she has competed as a pro, remaining ahead of her contemporaries. She led the cohort in the recent six-month period, mainly by reaching the final eight at U.S. Open 2014, where she defeated top-tenners Kerber and Jankovic. Otherwise, victories have been few against the older and stronger players that she increasingly faced as her world ranking improved, however, and 2015 brought mainly first-round losses including a one-sided losing score against Venus Williams at Dubai in late February. The latter affair exposed the huge gap that lies ahead for top junior players. Trained by the mother of Martina Hingis, Belinda's playing style has been compared to that of Martina.
 
Katerina Siniakova scored well in late 2014, winning ITF-circuit tournaments in Nantes and emerging from the qualifiers to reach the semis at the main-tour event at Moscow and the final 32 at Linz in late 2014. Her pattern in 2015 has been that of first-round wins and second-round losses against top-hundred opponents, including at Australian Open.
 
From a distant world ranking in the #800's, Oceane Dodin burst upward in mid-2014, assembling three triumphs in lower-level ITF-circuit tournaments during May-July. Her rise accelerated with a triumph at the mid-level ITF event in Shrewsbury, Britain, a final-round finish at the $100,000 ITF in Poitiers, and a semi-final finish at the Limoges $125,000. Wins against top-hundred and second-hundred opponents thus began to accumulate, and another tournament triumph came in Poland in November. Wild-carded into Australian Open 2015, she split even in two three-setters against top-fifty opponents.
 
Elizaveta Kulichkova continued a strong early career by winning Australian Open Juniors singles and doubles in 2014 at age 17. Already, she had shown success in ITF pro circuit tournaments, of which she has now won five including the most recent at Bangkok in October 2014. Since then she has competed exclusively in main-tour events including qualifiers, winning about half her matches generally against opponents in the second hundred.
 
Ana Konjuh joined Belinda Bencic in each winning two of the four Junior Slams of 2013. Elbow surgery in 2014 slowed her progress since then. Catherine (CiCi) Bellis is slightly behind Konjuh in our tally here at age not yet 16. CiCi earned acclaim at U.S. Open 2014 for skills and results amazing for her age. Though she is too young to play an unlimited schedule, she won the recent ITF-circuit tournament in Rancho Santa Fe, California.
 
THE 21-AND-UNDERS
 
Players 21-and-Under. Six-month ranking (Sep 14-Feb 15)
1. Eugenie Bouchard, age 21, height 5-10, (Canada), score 20.8
2. Garbine Muguruza, 21, 6-0 (Spain), 19.9
3. Zarina Diyas, 21, 5.8 (Kazakhstan), 19.0
4. Elina Svitolina, 20, 5-9 (Ukraine), 16.6
5 .Saisai Zheng, 21, 5-5 (China), 15.7
6. Madison Keys, 20, 5-10 (USA), 14.4
 
This is an unusually strong cohort, listing no teenaged penetrators from below through the top six places.
 
The remarkable success of Eugenie Bouchard in the Slams of 2014 was one of the big stories in pro tennis last year. Much was expected of Eugenie in 2015, so that her uncomfortable loss to Sharapova in the quarters at Australian Open seemed to many a disappointment. But that result -- along with three wins at U.S. Open 2014 and a final-round finish at the WTA event in Wuhan -- was enough to lift Eugenie again to first place among her contemporaries in our six-month tally. The strong stroking, the attacking mentality, the on-court composure, all in a player suddenly thrust onto the global spotlight, have been noteworthy.
 
The next five are not very far behind in our tally. All seem capable of and ready for competing at higher level. Climbing fast is Garbine Muguruza, who scored wins over Errani and A Radwanska in January and took Serena Williams to three sets at Australian Open. She then defeated Halep in Fed Cup and reached the semis at Dubai. Zarina Diyas climbed from eighth place in the preceding period to third place here, showing a recent pattern of wins exceeding losses in main-tour main-draw action, including two wins at Australian Open 2015. Elina Svitolina's recent pattern has been similar, including a win over top-tenner Kerber in Brisbane and winning a set from Serena Williams at Melbourne Park. Saisai Zheng defeated Zarina in reaching the semis in Shenzhen in January. Madison Keys achieved wide acclaim in marching to the semis at Australian Open 2015 behind extreme power in serving and stroking. Soon afterwards she moved out of the teenaged cohort upon her twentieth birthday in February.
 
THE 23-AND-UNDERS
 
Players 23-and-Under. Six-month ranking (Sep 14-Feb 15)
1. Karolina Pliskova, age 22, height 6-1 (Czech Republic), score 43.1
2. Simona Halep, 23, 5-6 (Romania), 38.3
3. Eugenie Bouchard, 21, 5-10, (Canada), score 20.8
4. Garbine Muguruza, 21, 6-0 (Spain), 19.9
5. Zarina Diyas, 21, 5-8 (Kazakhstan), 19.0
6. Elina Svitolina, 20, 5-9 (Ukraine), 16.6
 
Our two leaders here, Simona Halep and Karolina Pliskova, met each other in the final round at Dubai, U.A.E. in late February. Halep had been first-seeded and had won her earlier four matches in the tournament while losing only one set. Simona had already broken into the world's first ten and was now well seasoned against top players.
 
Pliskova, on the other hand, had required third sets in three of her victories (against Ivanovic, Safarova, and Muguruza) and was a relative newcomer to high place. Her upward move had strongly accelerated during the six-month period of our review, up from eighth place in the cohort during the preceding six months. Already showing seven wins over top-25-ranked opponents in the first two months of 2015 and at an official world rank of #18, her readiness to close on the first ten seemed clear. Tall and slender, Karolina had been second in 2014 in producing aces among all female pros, behind only Serena Williams. (She was ahead of Serena for 2015 albeit Serena's having played in fewer events.) Twin-sister Kristyna is left-handed (Karolina is a righty), and the sisters have regularly competed in doubles.
 
For one set the pattern was straightforward. Halep had trouble returning the big serves of Karolina, but otherwise it was hard for Karolina to win points. Simona was better at sustaining rallies, was more accurate in her attacking, and --probably most important of all -- was brilliant in fending off Karolina's rockets whenever one of them found a corner. Matters became more fluid in the second set, as Simona became better at returning serve effectively, while Karolina's flat ground strokes began to find their targets more regularly. Karolina's serve thus became less a factor, but Karolina's ground game improved enough to force tiebreaker, won by Halep. The affair confirmed Karolina's excellent serving power and accuracy, and it also showed that the tall Czech player could readily improve by using more topspin to control her extreme ground-stroke power and by stepping forward more quickly to attack short balls. Halep d. Pliskova 64 76.
 
The match provided an interesting though hardly decisive test for our six-month scoring scheme. There was little doubt that in their meeting Halep showed the better current playing ability. Thus in this match-up Halep's edge over Pliskova in 12-month official ranking proved the better predictor than Pliskova's edge in our six-month count. Wider analysis for our method is needed, perhaps weighting past outcomes to favor recency along with using a longer measuring period. (Our Monster Spreadsheet can readily employ almost any design.)
 
Four younger players from the 21-and-under cohort complete our 23-and-under top six. That phenomenon indicates that the most talented of our women's cohorts is that of the 21-and-unders.
 
All five leaders of the 23-and-under female cohort have already penetrated at least the world's top fifty. All five have shown readiness for penetration into the world's first ten -- Halep is already there, and Bouchard attained that honor temporarily last year. The power games of Pliskova and Muguruza lend extra evidence to their top-ten credentials, and the talents of Zarina Diyas resemble and are not far behind those of Halep. Thus all five have already exceeded the indicated probabilities offered at the start here.
 
The top leaders of our six male and female cohorts tallied for the last six months were in many cases also leaders in the preceding six months. The consistency is most notable in the boys' teenaged cohort and in the girls' 21-and-under cohort, where in both cases three players are among the top four in both periods. All other cohorts show two repeaters in their top fours, except the male 23-and-under cohort, which misses that result by only one ranking place by one player. Moderate commonality across the six-month tallies is also detectable among the top tens within all cohorts. Our tallies thus indicate moderate stability in rank order among the young risers during their years of upward journey.
 
All our listees have come a long way since entering international junior competition. Will any of them, male or female, manage the huge jump to world's #1, becoming the acknowledged Il Primo or La Prima of pro tennis? That will require his or her continuation, indeed intensification, of the enormous sacrifices and efforts that all have made ever since early success among the juniors.
 
--Ray Bowers, Arlington, Virginia, U.S.A.
 
FOOTNOTES
 
Here are a few examples especially pertinent in calculating our six-month tallies identifying the young risers. Values awarded for various successes are shown.
 
-- Challenger tournaments (and upper-level women's ITF pro circuit events). (Examples: 1.2 pts for winning lowest-level Challenger event, 0.7 to runner-up; 2.7 pts for winning highest-level Challenger event, 1.7 to runner-up. Lesser values are awarded to those attaining lesser rounds.)
 
-- qualifying rounds of main-tour events (Examples: 0.9 pts for winning three qualifying matches and advancing to main draw. 0.5 pts for winning two but then losing.)
 
-- match wins at main draws of Slams (Example: winning first round earns 1.1 pts, second round additional 1.4 pts., total 2.4 etc.)
 
Credit: The list of Junior Slam champions used here is from Wikipedia.