With the first five weeks of the 2021 season in the books and the champions crowned at six events, WTA Insider breaks down the season's statistical leaders as the tour leaves Melbourne. Stats based on a minimum of 5 main draw tour-level matches and do not include active tournament results. Stats and information provided by SAP Sports. All data as of Monday, February 22, 2021.

Tournament Champions
Abu Dhabi: Aryna Sabalenka d. Veronika Kudermetova
Yarra Valley Classic: Ashleigh Barty d. Garbiñe Muguruza
Gippsland Trophy: Elise Mertens d. Kaia Kanepi
Grampians Trophy: Anett Kontaveit, Ann Li (Co-champions)
Phillip Island Trophy: Daria Kasatkina d. Marie Bouzkova
Australian Open: Naomi Osaka d. Jennifer Brady

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Most Match Wins
1. Naomi Osaka - 10-0
2. Daria Kasatkina - 10-3
3. Aryna Sabalenka - 9-2
T-4. Garbiñe Muguruza - 9-3
T-4. Jennifer Brady - 9-3

Rising to No.2 after her Australian Open win, Naomi Osaka extended her active winning streak to 21 consecutive matches. She has not taken a loss in over 12 months.

Daria Kasatkina matches Osaka's 10 wins after a grueling run to the Phillip Island Trophy, which saw the Russian win six matches to win her first title since 2018 Moscow. 

Most Top 10 Wins
T-1. Karolina Muchova - 2-0 (Ka.Pliskova, Barty)
T-1. Kaia Kanepi - 2-0 (Sabalenka, Kenin)
3. Serena Williams - 2-1 (Halep, Sabalenka)

Australian Open semifinalists Karolina Muchova and Serena Williams join Gippsland Trophy runner-up Kaia Kanepi with two Top 10 wins apiece. Serena's back-to-back wins over Simona Halep and Aryna Sabalenka at the Australian Open were masterclasses in the American's improved movement, while Kanepi's dominant wins to end Sabalenka's 17-match winning streak and knock defending champion Sofia Kenin from the Australian Open were notably seismic.

Muchova tallied the two most dramatic wins, rallying from 0-5 down in the second set to close out her compatriot Karolina Pliskova and overcome a set and a break deficit to No.1 Ash Barty to oust the Aussie from her home Slam. 

Russian No.1 Ekaterina Alexandrova has hit a tour-leading 73 aces in 10 matches in 2021.

Photo by Tennis Australia

Ace Leaderboard
1. Ekaterina Alexandrova - 73
2. Naomi Osaka - 68
3. Jennifer Brady - 60
4. Ashleigh Barty - 59
5. Veronika Kudermetova - 55
6. Ons Jabeur - 53
T-7. Serena Williams - 51
T-7. Karolina Pliskova - 51
9. Maria Sakkari - 49
10. Aryna Sabalenka - 47

No.33 Ekaterina Alexandrova has enjoyed a strong start to 2021, with wins over Iga Swiatek and top-seeded Halep en route to the semifinal of the Gippsland Trophy. Firing an average of 7 aces per match certainly helps her cause.

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Average Aces per Match
1. Rebecca Marino - 7.4
2. Ekaterina Alexandrova - 7.3
3. Karolina Pliskova - 7.29
4. Heather Watson - 6.8
5. Ons Jabeur - 6.6

Welcome back, Rebecca Marino. After leaving the game in 2019, the Canadian returned to qualify for her first Slam main draw since 2013 Australian Open and earned her first main draw win at a Slam in nearly a decade. Her big serve proved a valuable weapon on the quick courts at Melbourne Park. 

2021 Australian Open champion Naomi Osaka leas the tour in both Service Games Won and First Serve Points Won.

Photo by Getty Images

1st Serves Won
1. Naomi Osaka - 78.7%
2. Serena Williams - 77.0%
3. Jennifer Brady - 76.3%
4. Rebecca Marino - 74.2%
5. Ashleigh Barty - 74.1%
6. Elena Rybakina - 74.0%
7. Ons Jabeur - 72.9%
8. Shelby Rogers - 72.2%
9. Ekaterina Alexandrova - 71.7%
10. Aryna Sabalenka - 70.9%

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2nd Serves Won
1. Shelby Rogers - 58.8%
2. Marie Bouzkova - 55.7%
3. Karolina Muchova - 55.0%
4. Caroline Garcia - 53.7%
5. Rebecca Peterson - 53.5%
6. Naomi Osaka - 53.2%
T-7. Jennifer Brady - 52.2%
T-7. Kaia Kanepi - 52.2%
9. Jasmine Paolini - 51.6%
10. Elena Rybakina - 51.5%

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Service Games Won
1. Naomi Osaka - 82.2%
2. Ashleigh Barty - 81.1%
3. Rebecca Marino - 78.2%
4. Vera Zvonareva - 77.3%
5. Kaia Kanepi - 77.0%
6. Jennifer Brady - 75.6%
7. Elena Rybakina - 75.0%
8. Marta Kostyuk - 74.1%
9. Aryna Sabalenka - 73.5%
10. Serena Williams - 73.5%

Of the players who feature on the leaderboard for 1st serves won and 2nd serves won, only Naomi Osaka, Jennifer Brady, Elena Rybakina, and Shelby Rogers land on both Top 10 lists.

Kaja Juvan saved 13 of 16 break points en route to a gritty second-round win over Mayar Sherif at the Australian Open.

Photo by Tennis Australia

Break Points Saved
1. Kaja Juvan - 66.0%
2. Kaia Kanepi - 64.3%
3. Sara Errani - 61.5%
4. Marta Kostyuk - 59.6%
5. Hsieh Su-Wei - 59.0%
6. Ashleigh Barty - 58.5%
7. Naomi Osaka - 58.1%
8. Kimberly Birrell - 56.8%
9. Leylah Fernandez - 55.9%
10. Marketa Vondrousova = 55.0%

20-year-old Slovenian Kaja Juvan lands at the top of the leaderboard in break points saved, thanks in large part to her clutch effort against Mayar Sherif in the second round of the Australian Open. In a physically punishing match, Juvan saved 13 of 16 break points over the course of a 3-6, 7-6(2), 6-3 win to advance to her first third round at a major. 

Sara Errani during her second-round match against Venus Williams at the 2021 Australian Open.

Photo by Getty Images

1st Serve Return Points Won
1. Sara Errani - 47.6%
2. Sara Sorribes Tormo - 45.5%
3. Zhu Lin - 45.1%
4. Garbiñe Muguruza - 44.1%
5. Maria Sakkari - 43.6%
6. Ashleigh Barty - 42.8%
7. Nadia Podoroska - 41.7%
8. Marta Kostyuk - 41.7%
9. Daria Kasatkina - 41.6%
10. Ann Li - 41.5%

Ranked No.106, two-time Roland Garros finalist Sara Errani has set the early benchmark for First Serve Return Points Won as well as Return Games Won (see below). Errani's 6-1, 6-0 win over Venus Williams in the second round of the Australian Open saw Errani break serve six times and win over 50% of first serve return points in a match that saw Venus injure her knee. 

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2nd Serve Return Points Won
1. Elise Mertens - 64.6%
2. Ajla Tomljanovic - 63.9%
3. Sara Errani - 62.5%
4. Naomi Osaka - 61.6%
5. Danielle Collins - 59.8%
6. Marta Kostyuk - 59.7%
7. Aryna Sabalenka - 59.6%
8. Anastasia Potapova - 59.5%
9. Sara Sorribes Tormo - 59.4%
10. Aliaksandra Sasnovich - 59.3%

Break Points Converted
1. Elise Mertens - 67.3%
2. Katie Boulter - 66.7%
3. Kaia Kanepi - 59.3%
4. Marta Kostyuk - 56.9%
5. Elena Rybakina - 54.3%
6. Daria Kasatkina - 54.0%
7. Ann Li - 54.0%
8. Naomi Osaka - 53.8%
9. Danielle Collins - 52.8%
10. Tamara Zidansek - 52.6%

With a title at the Gippsland Trophy and run to the Round of 16 at the Australian Open, Elise Mertens continues to cement herself as one of the tour's most reliable tournament players. Since the tour resumed last summer, Mertens has played with more aggression from the baseline while continuing to build her reputation as one of the tour's elite returners. Last season, the Belgian was behind only Simona Halep in Return Games Won (41.4%) and she continues to be a threat this season. Mertens finished the 2020 season at No.3 in Break Points Converted (49.0%).

Garbiñe Muguruza has broken serve 50.9% of the time, the second-best break rate on tour.

Photo by Getty Images

Return Games Won
1. Sara Errani - 59.6%
2. Garbiñe Muguruza - 50.9%
3. Sara Sorribes Tormo - 50.6%
4. Elise Mertens - 47.9%
5. Marta Kostyuk - 47.4%
6. Aryna Sabalenka - 46.4%
T-7. Zhu Lin - 45.8%
T-7. Ann Li - 45.8%
9. Danielle Collins - 45.5%
10. Naomi Osaka - 44.7% 

Interestingly, while the majority of the serving categories feature 3-4 Top 10 players on the leaderboard, the return statistics are not dominated by the tour's top players. No more than two members of the Top 10 appear on any given return of serve leaderboard.

This will be a trend to track as the season unfolds. By way of comparison, 3 Top 10 players were in the season-ending Top 10 in Service Games Won last season (Kvitova, Kenin, Sabalenka), and 4 finished in the Top 10 among Return Games Won (Halep, Kvitova, Sabalenka, Svitolina).