Here’s a stat you probably didn’t know*. Since the restart, the WTA top five in first-serve points won are Naomi Osaka, Serena Williams, Ashleigh Barty, Jennifer Brady, and … Maria Sakkari.
** unless you’ve been listening to me podcast lately.
The first four names are to be expected: Osaka, Williams, and Barty are probably the top three offensive players in the game, period, and Brady makes her money with big serving. Sakkari is the one who stands out. She does many things well, but I would never have thought to put her in this group, ahead of the likes of Karolina Pliskova, Aryna Sabalenka and, well, everybody else.
Sakkari’s first serve might be the best-kept secret in the women’s game, in large part because it hasn’t been around to keep secret for long. When she started playing tour events, her serve was quite weak, and it has only gradually improved since then. That’s what I marvel at. In six seasons at tour level, all with at least 18 matches played, here are her rates of first-serve points won:
Year 1st Win%
2016 58.6%
2017 59.7%
2018 63.7%
2019 65.2%
2020 66.5%
2021 69.9%
This probably doesn’t need further explanation. Fewer than 60% of first serve points isn’t very good, 70% is excellent, and improving from one to the other is a massive accomplishment. But in case you’re not convinced, here’s the same progression along with percentile rankings, showing that Sakkari started her career better than only 13% of her peers, and this year is outperforming 93% of them:
Year 1st Win% Percentile
2016 58.6% 13
2017 59.7% 20
2018 63.7% 53
2019 65.2% 67
2020 66.5% 79
2021 69.9% 93
Players can and do improve, but they usually retain the same relative strengths and weaknesses throughout their career. The Greek star has broken that mold, and there’s a natural follow-up question: Has there been anyone else like her?
Meet Kiki
Here’s the simple filter I used to identify players who had substantially improved this aspect of their game. For every player with a full season in which they won fewer than 60% of first-serve points (almost exactly the 20th percentile), I identified those who eventually recorded a full-season in the top half of WTA players, roughly 63.3% or better.
From 2010 to 2021–yes, an awfully short span, due to the limited availability of historical WTA match stats–112 different players posted a sub-60% season. 26 of them went on to an above-average year. One example is Carla Suarez Navarro, who won 59.0% of first-serve points in 2010, and peaked at 64.0% (56th percentile) in 2016. That’s a respectable progression, but far from Sakkari’s standard.
Here are the 10 players who improved on a sub-60% season to eventually manage a season of 65% or better, ranked by the best level they attained:
Player Weak 1st% %ile Strong 1st% %ile
K Bertens 2015 59.5% 18 2019 71.9% 97
M Sakkari 2016 58.6% 13 2021 69.9% 93
D Kasatkina 2017 59.0% 15 2021 66.4% 78
S Halep 2012 56.4% 3 2014 66.4% 78
Y Shvedova 2011 59.4% 17 2016 66.1% 75
A Cornet 2011 58.9% 14 2020 66.1% 75
M Linette 2016 59.9% 21 2020 65.8% 73
Y Wickmayer 2012 60.0% 22 2017 65.8% 72
A Sasnovich 2016 58.4% 11 2018 65.1% 67
S Stephens 2011 59.7% 19 2015 65.0% 66
Kiki Bertens wasn’t quite as bad as Sakkari at her worst, but she wasn’t getting much benefit from her first serve. Like the Greek, she had back-to-back seasons below 60%, but unlike Sakkari, her improvement was instant. She leapt from sub-60% in 2015 to almost 68% (86th percentile) a year later. You won’t be surprised to hear that her ranking catapulted upwards as well, from 104th at the end of 2015 to 22nd a year later.
Kiki’s several years since also bode well for Sakkari. Her first-serve winning percentage of 67.4% last year was her worst since crossing the 60% barrier. A slightly less optimistic story comes from Simona Halep, whose 78th percentile mark in 2014 remains her career best. Coming from such an abysmal starting point, it’s remarkable that Halep has improved as much as she has, but she remains firmly in the range of good-but-not-great in this dimension of her game.
Steady improvements
There’s no particular advantage to spreading out one’s gains over a half-decade, like Sakkari has. If she had been given the option of picking up eight percentage points in a single year, like Bertens did, she would’ve taken it.
Still, the fact that the Greek keeps marching upwards is what makes her ascent so fascinating to me. In the decade-plus of data available, no other woman has improved her first-serve win percentage for five years running. Only two players–Yulia Putintseva and Saisai Zheng–have enjoyed positive bumps for four consecutive seasons, and neither situation really compares. Zheng’s improvement took her from 53.2% in 2015 to 59.3% in 2019, and Putintseva rose from 57.9% in 2017 to 62.4% so far this year. While both are making the most of what they have, neither has fundamentally transformed the type of threat they bring on court the way that Sakkari has.
In search of a better comparison–any comparison–with this five-year streak of gains, I turned to the more extensive set of ATP match stats, which go back to 1991. In those three decades, I found exactly 10 players who improved in this department for five (or more) consecutive years. It’s a decidedly diverse group, with a few names you might recognize:
Player Streak Start %ile End %ile
Renzo Furlan 6 2 73
Slava Dosedel 6 2 16
Julien Benneteau 5 16 55
Arnaud Clement 6 18 70
Michael Chang 5 18 92
Roger Federer 5 47 94
Thomas Enqvist 5 58 94
Boris Becker 6 79 99
John Isner 7 82 98
Marc Rosset 5 87 98
The starting and ending percentiles indicate that this list includes players who began bad and ended a bit less bad, servebots who started great and eked even more out of their biggest weapon, and then a handful of Sakkari-esque figures who steadily went from considerably below average to far above it.
Michael Chang is the closest parallel of the group, even if we don’t have complete match stats for the first few years of his career. In 1991 he was one of the best returners in the game, but winning barely two thirds of his first serve points wasn’t enough to keep him in the top ten in an offense-dominated era. Five years later he was winning 77% of his first deliveries and ended the season at his peak ranking of #2. He couldn’t sustain the elite-level serving stats, but he did have a few more above-average years.
And then there’s Roger Federer. I’ll leave it to Sakkari fans to work out whether his presence on this list can tell us anything about her future.
Ave Maria
This is all just a long way of saying “wow!” There are other aspects of Sakkari’s game that she has improved, though none so consistently and dramatically. Once you start looking at year-to-year trends for individual stats, future projects start to multiply: identifying peak ages for different parts of the game, determining which stats are more or less likely to regress to the mean, finding which ones best predict ranking climbs, and so on.
We’ll get to some of those answers eventually. In the meantime, I’ll be watching Sakkari with new, better-informed eyes.
