Three players from last year's top 20 are no longer teenagers, opening the door for some of the world's best young guns to make the list for the first time. In the nearly three years of doing this series, it has only gotten harder to narrow the field down to 20 as players continue to play better at earlier stages in their careers.
Here's a look at the last four lists of the top 20 under 20.
Previous Top 20 Under 20
| No. | Feb. 2015 | July 2015 | Feb. 2016 | Aug. 2016 |
| 1. | Nick Kyrgios | Borna Coric | Alexander Zverev | Alexander Zverev |
| 2. | Borna Coric | Andrey Rublev | Borna Coric | Taylor Fritz |
| 3. | Roman Safiullin | Alexander Zverev | Taylor Fritz | Borna Coric |
| 4. | Andrey Rublev | Jared Donaldson | Frances Tiafoe | Frances Tiafoe |
| 5. | Jared Donaldson | Hyeon Chung | Felix AA | Denis Shapovalov |
| 6. | Alexander Zverev | T. Kokkinakis | Hyeon Chung | Jared Donaldson |
| 7. | Hyeon Chung | Taylor Fritz | Andrey Rublev | Felix AA |
| 8. | Y. Nishioka | Frances Tiafoe | Jared Donaldson | Andrey Rublev |
| 9. | T. Kokkinakis | Elias Ymer | Roman Safiullin | Reilly Opelka |
| 10. | Elias Ymer | Roman Safiullin | T. Kokkinakis | M. Kecmanovic |
| 11. | Christian Garin | Omar Jasika | Elias Ymer | Stefan Kozlov |
| 12. | Noah Rubin | Laslo Djere | Duckhee Lee | Stefanos Tsitsipas |
| 13. | Frances Tiafoe | Y. Nishioka | Oliver Anderson | Michael Mmoh |
| 14. | Taylor Fritz | Mikael Ymer | Karen Khachanov | Quentin Halys |
| 15. | Stefan Kozlov | Tommy Paul | Rayane Roumane | Casper Ruud |
| 16. | Seong Chan Hong | Reilly Opelka | Stefanos Tsitsipas | Alex De Minaur |
| 17. | Duckhee Lee | Stefan Kozlov | M. Kecmanovic | Tommy Paul |
| 18. | Ernesto Escobedo | M. Kecmanovic | Quinten Halys | Rudolf Molleker |
| 19. | Yun Seong Chung | Stefanos Tsitsipas | Duckhee Lee | Duckhee Lee |
| 20. | Noah Rubin | Felix AA | Michael Mmoh | Zane Khan |
Link: First edition (July 2014)
1. Alexander Zverev (GER) Age: 19, Rank 20
Zverev is not only in the top 20 for this age group. The German is in the top 20 in the world for any age and has been as high as No. 18 this year. It wasn't long ago that there wasn't a single teenager anywhere in the top 200, let alone the top 20. A couple weeks ago, Zverev earned his second career title, beating Jeremy Chardy, Jo-Wilfried Tsonga and Richard Gasquet along the way on French soil. At the Australian Open, Zverev reached the third round and led two sets to one before falling to the eventual runner-up Rafael Nadal. He's 6-foot-6 and moves better than anyone else his size. There aren't many weaknesses in his game, but opponents will be trying to uncover any weakness for years to come. He's the player to beat in the next generation.2. Taylor Fritz (USA) Age: 19, Rank 136
3. Frances Tiafoe (USA) Age: 19, Rank 86
Tiafoe joins Zverev as the lone teenagers inside the top 100 right now. The young American has been surrounded by hype for years because of his lightning-quick speed and his power off the forehand wing. Despite his athleticism, Tiafoe has several technical flaws in his game. His serve has a big pause right in the middle of the motion, his backhand looks stiff and his forehand is awfully flat for such a wrist-driven action. It is almost impossible to make big technical changes to a game at this point in his career, which could put a ceiling on just how successful he could be. Still, he's already in the top 100 and can only get better from here, so it's hard to leave him out of the top three.4. Felix Auger-Aliassime (CAN) Age: 16, Rank 511
5. Casper Ruud (NOR) Age: 18, Rank 128
After a remarkable junior career, Ruud has had little trouble adjusting to life as a professional. Ruud won his third event of the 2016 season, a futures in Paguera, Spain, and he hasn't looked back since and is now knocking on the doorstep of the top 100. He is the first player on this list so far that prefers clay, but he isn't just a clay specialist. He already has three tour-level victories on hard courts and was one win away from qualifying for the Australian Open. Clay is clearly his preferred surface though and he is currently the King of Yellow Clay after winning the Challenger in Sevilla as a qualifier, coming back from down a set four times. Ruud moves well, making it hard for opponents to get to his backhand and he's able to strike the ball well from defensive positions. Ruud reached the semifinals in Rio and will be hoping to get some wild cards during the spring to test his ability against the best during the European clay swing.6. Denis Shapovalov (CAN) Age: 17, Rank 253
The 2017 season hasn't been kind to Shapovalov, who looked to be on a clear path to the top 200 just a few months ago. Still, he is by far the highest ranked player of his age group and is one of the only left-handed players his age that is having success. His unique style with the nasty slice serve along with a one-handed backhand will make him tricky to beat even though he lacks any single massive weapon. He has great hands, which makes up for the awkwardness of one-handed returns. At his best, he is a left-handed Stan Wawrinka with great court coverage. The key for the Canadian will be to get more consistent power on his ground strokes, especially the forehand. He's only 17, so there is plenty of time to improve his game before he starts contending for tour-level titles on a weekly basis. 7. Andrey Rublev (RUS) Age: 19, Rank 134
It has been nearly two years since Rublev first cracked the top 200 and he still hasn't reached the top 100 just yet. He reached a career-high ranking of 111 after qualifying for Marseille, but the lack of progress for the Russian has been worrying. He is currently No. 49 in the Race to London rankings, which is a good sign after some success on the Challenger Tour. Rublev prefers hard courts, but has been successful on clay as well. He won't be getting as many wildcards now as he was last year, so he's going to have to work his way into the top 100. Once he gets that breakthrough, that could be what opens the flood gates that hold back all the potential that he clearly possesses. His big breakthrough has taken longer than expected, but there are still lots of reasons to be excited about Rublev's future.8. Reilly Opelka (USA) Age: 19, Rank 169
Approaching seven-feet tall, Opelka is guaranteed to have a very successful career if he stays healthy. The blueprint for success has already been laid out for tennis' tallest player by Ivo Karlovic and John Isner. Opelka already has a more complete game than either of those players, moving very well for his size with technically solid ground strokes. He tends to pull the trigger early in the rally from bad positions rather than trusting his ability to win long rallies. But when you serve like Opelka, you're only looking for one break each set anyways. There isn't much harm in going for broke when he only has to be successful once in six tries. Neither of his peers in height have been able to grab the biggest trophies in tennis though. Five sets is tough for a player that relies primarily on his serve, especially when there is no tiebreaker in the fifth. That's where Opelka's return game is going to have to come through for him. He already has a great second-serve return, so he just needs to get his timing down on the first serve. Isner has a notoriously late split step on first serve returns, which will be something that Opelka will learn from.9. Stefan Kozlov (USA) Age: 19, Rank 116
10. Alexander Bublik (KAZ) Age: 19, Rank 138
The biggest mistake on my list last summer arguably was leaving Bublik off the list. As soon as the list came out, he went on to win two of the next three futures events he played in and then reached the quarterfinals in Moscow as a qualifier. Then he reached the second round of the Australian Open was a qualifier after knocking off No. 16 Lucas Pouille in the first round to crack the top 200. In February, he won a Challenger Tour event in Mexico and is now at a career-high ranking of 138. Bublik has a great serve and forehand, but movement and shot selection are his weaknesses. He favors his forehand so much that he tries to run around everything, jamming himself often. His backhand actually isn't that bad when he has his feet set. If he stops running around his backhand or hitting drop shots and tweeners from bad positions, he'll win a lot more matches. Tactical adjustments are the easiest kind to make. If he has a good coach in his corner throughout his career, he'll make me look even more foolish for leaving him off the list last time.11. Miomir Kecmanovic (SRB) Age: 17, Rank 651
The Serb is exactly 200 spots higher than he was when the fifth edition came out, which is good progress. He started the year with a great result in Sunrise, Florida, winning the futures event against a tough field. He has gone into a slump since then, which is the problem with playing futures events exclusively in the United States. There is no such thing as an easy draw aside from his first-round match against a player that has never been ranked in singles after finishing his collegiate career in 2010. The Serb has also played only clay events this year despite having some success on hard courts last year. Kecmanovic has lots of time to develop, so his ranking doesn't need to be his top priority right now.12. Duckhee Lee (KOR) Age: 18, Rank 135
The Korean keeps making it harder for me to leave him this low on the list with every passing edition, but he still hasn't tested himself against the best players in the world. He has pushed himself more in his scheduling this year, which is a good sign, but he hasn't had any great wins yet. He beat clay specialist Nicolas Kicker in the first round of qualifying at the Australian Open. Lee also beat Lukas Rosol and Daniel Brands in a Challenger Tour event which helps justify his ranking. He has a very smooth game, but doesn't have any weapons that can make him successful on the next level. His prospects aren't very high, but it is hard to ignore an 18-year old with his ranking.13. Stefanos Tsitsipas (GRE) Age: 18, Rank 206
The potential savior of serve-and-volley tennis is getting closer to making his big break through. He cracked the top 200 temporarily and had two very solid showings on indoor hard courts in February despite the losses. He is scheduling the toughest events, so his win-loss record right now isn't great, but he could easily go play lower-level events to boost his ranking. Tsitsipas is more concerned with testing his game against the best players in the world and this will help him develop quickly this season. It's great to see a player his age with such a well-defined game plan every time he steps onto the court, forcing opponents to adjust to his style of play. The big question will always be if that style can ever work again on the tour-level. Tsitsipas is the ultimate experiment of serve-and-volley tennis among professionals.14. Alex De Minaur (AUS) Age: 18, Rank 262
I held off on putting De Minaur on this list last year and hesitantly put him on the list last summer, but this time around it's a no-brainer. De Minaur made a splash during the Australian summer with wins over Mikhail Kukushkin, Frances Tiafoe and Benoit Paire to start the season. Then in front of a packed stadium, came back from two sets to one in defeating Gerald Melzer at the Australian Open. De Minaur hasn't played outside of his home country yet this year and that could be when we really get a sense of just how good he is, but he's off to a great start in 2017.15. Michael Mmoh (USA) Age: 19, Rank 185
Mmoh has made a home for himself in the top 200 in the last few months with a handful of attention-grabbing wins in 2017. He opened with a win against Grega Zemlja and then beat Greg Jones and Jerzy Janowicz down under. He has gone 6-3 in Challenger Tour events in the United States since then to reach a career-high ranking of 182. He is No. 73 in the Race to London Rankings with the help of his win in Knoxville to finish 2016. Mmoh has a great forehand and a lot of quickness around the court. His serve is excellent when he is making a high percentage, which gives him a reliable formula for success moving forward. He is one of many Americans that could be dominating the tour over the next 10 to 15 years. There's plenty to be excited about for American tennis fans.16. Roman Safiullin (RUS) Age: 19, Rank 411
Safiullin's career so far has been plagued by injuries, so he may take a lot longer than most players to reach his full potential. Hopefully injuries don't derail his whole career, because he has a very complete game that would be fun to watch at the highest level. Along with Khachenov and Rublev, the three Russians provide a hopeful future for tennis in the country. He has played qualifying for two Challenger events this year and picked up a pair of wins, but not any ranking points. If he drops down to the futures level, nobody will want to see their name next to his in the draw. Hopefully he will be healthy at some point this season, so that he can build his ranking back up to where it should be this year.17. Marc Polmans (AUS) Age: 19, Rank 225
If there were a doubles version of this list, Polmans would be No. 1 after reaching the semifinals at the Australian Open in doubles. His singles game isn't at the same level, but his doubles success is still a very positive sign. He tends to rely a lot on the slice on the backhand side, but when he hits his backhand moving forward, it is a very effective shot. There's a big gap right now between the first and second serves, which can easily be improved. For someone so successful in doubles, he doesn't spend much time at the net in singles, which isn't necessarily a bad thing. Polmans can finish points from the baseline, which is good news for the Australian.18. Corentin Moutet (FRA) Age: 17, Rank 440
Moutet reached the quarterfinals of Cherbourg as a qualifier for the best result of his career to date as a professional. A 5-foot-9 left-hander, he looks like his game would be similar to that of Yoshihito Nishioka, but the Frenchman plays a very distinct style. Moutet has great ground strokes, but lacks the movement to hang with a lot of players from the baseline. His touch and his ball-striking at the baseline usually sets him up well when he does come to net. It is unique to be 5-foot-9 and want to end points quickly, but that will change as he develops physically to become more athletic. Once he improves his game defensively, he'll be much tougher to beat.19. Tommy Paul (USA) Age: 19, Rank 327
No player wants to go from the top 200 to playing in futures events, but that's what Paul had to do after his slump pulled his ranking down as low as 318. Paul responded by winning the futures title in Palm Cost, USA with just two sets dropped along the way. A number of players over the years have struggled to deal with the pressure of being a young successful player in the United States. Paul still has his whole career ahead of him and has already shown positive signs in his career. His best quality is his ability to win on any surface, which doesn't become useful until you reach the tour-level, but it's always nice to have in his back pocket. Once he gets inside the top 100, he won't leave for a long time.20. Nicola Kuhn (ESP) Age: 16, Rank 718
It's always hard to figure out who to finish this list with, but Nicola Kuhn is a tough one to miss since the future of Spanish tennis rides on his back. Spain has been the best tennis country for more than the last decade, but recently has dropped behind France in that distinction. Kuhn is the one that could change that. He is a unique Spaniard in that he prefers hard courts, which is where all five of his futures level wins this year have come from. Kuhn is ow a professional full time after playing a few Grade A events in the second half of the 2016 season. He reached a career-high ranking of No. 5 in the world in junior tennis. Kuhn results are impressive, but he is still having most of his success against players that aren't as talented as him. He has yet to start beating players that are on his level. 