Is Katerina Siniakova the best doubles player of the 21st century? The numbers make a strong case

On September 11, Katerina Siniakova was a set down in the US Open women's doubles final. An hour and 53 minutes later, she and Taylor Townsend had beaten wild cards Ashlyn Krueger and Robin Montgomery 5-7, 6-0, 6-2 to win the 12th Grand Slam doubles title of her career. It completed a career Grand Slam with Townsend, and made Siniaková the first player in history to complete the career Grand Slam with two different partners. She had done it the first time with Barbora Krejcikova in 2022.

She is 30 years old, currently world No. 1 in doubles for the seventh separate time, and in the middle of a season that has already brought seven titles. That is a lot of context for what should be a simple question: how good is she, really? The answer depends on which question you ask.

Is she the best doubles player of all time? No, and that title belongs to Martina Navratilova by a distance. Is she the best of this century, and where does she sit in the Open Era? That is a far more interesting debate, and the numbers make her case better than most people realize.

Siniaková’s rise began with a partnership. After winning her first WTA doubles title in Tashkent in 2014 alongside Aleksandra Krunić, she teamed up with compatriot Barbora Krejcikova. Together, they reached the French Open semi-finals in 2016, despite both players still being in the early stages of their careers at just 20 years old.

After their first two titles, Siniaková endured a series of disappointments, losing eight consecutive doubles finals alongside Krejcikova, Vera Dushevina and Lucie Hradecká. During that stretch, she also reached the US Open final in 2017 and appeared in two WTA 1000 finals. Despite consistently advancing to the latter stages of major tournaments, a significant breakthrough in the biggest events remained elusive.

That changed in 2018, when Siniaková and Krejcikova took another step forward. They won the French Open and Wimbledon, with their success culminating on October 22, 2018, when Siniaková became the world No. 1 in doubles for the first time at just 22 years old. On the same day, she reached her career-high singles ranking of No. 31, a coincidence that neatly captured her versatility. The pair finished the season as the year-end No. 1 team, while Siniaková also helped the Czech Republic win the Fed Cup. It was a rapid ascent, but only the beginning.

Siniakova and Krejcikova developed into an elite doubles partnership, regularly entering tournaments among the leading contenders. Their collaboration reached its peak between 2021 and 2023. In 2021, they won Roland Garros, where Krejcikova also claimed the singles title, and Olympic gold in Tokyo. They subsequently finished the year as the No. 1 team.

In 2022, the pair won three of the four Grand Slam titles, triumphing at the Australian Open, Wimbledon and the US Open. Their success at Flushing Meadows completed their career Grand Slam, having won all four majors together.

The US Open final saw them defeat Caty McNally and Taylor Townsend 3-6, 7-5, 6-1. That achievement also completed their Career Super Slam, which combines all four Grand Slam titles, Olympic gold and the year-end championships. They became the first women's doubles team to accomplish the feat and the third and fourth women overall to do so, following Gigi Fernández and Pam Shriver. Siniaková and Krejcikova added a seventh Grand Slam title together at the 2023 Australian Open.

What separates Siniaková from many great doubles players is that she did not need a single partner to keep winning. In 2024 she won Roland Garros with Coco Gauff. She had first teamed up with Townsend in Rome earlier that spring, and the pair won Wimbledon in only their third event together. They added the 2025 Australian Open, the 2026 Roland Garros and, on September 11, the 2026 US Open, completing a career Grand Slam in their first 10 majors as a pair.

She has been just as effective with other partners. This season she has also won Adelaide and Toronto with the Chinese veteran Zhang Shuai, and the pair carried a 13-match winning streak into the China Open final last Sunday, where Gabriela Dabrowski and Luisa Stefani beat them 6-1, 6-2. She also won a mixed doubles major at Wimbledon in 2025 in her first tournament with Verbeek, and Olympic mixed doubles gold with Tomas Machac in Paris in 2024, which makes her the only Czech to win two Olympic gold medals.

Her case is strongest where doubles is measured over the long run. By WTA and Wikipedia's count, Siniaková has now spent about 200 weeks at No. 1 in doubles, which puts her second in WTA history behind only Navratilova's 237. Liezel Huber is third with 199. She has done it across seven separate spells, and her longest unbroken run is 52 weeks, from September 2022 to September 2023.

She has also finished the year at No. 1 five times, tying Navratilova's record. Should she hold the top spot at the end of 2026, it would be her sixth, which would make her the first player in WTA history to pass Navratilova on that list.

The honest all-time answer is that she is not close to Navratilova, who won 31 women's doubles majors, 177 doubles titles and the career Grand Slam five times. After her come Pam Shriver (21 majors), Natasha Zvereva (18) and Gigi Fernández (17). Sinakova is one of only eight women to have won 12 or more doubles majors in the Open Era, a short list led by Navratilova.

The picture is different if the question is limited to the 21st century. Serena and Venus Williams won 14 doubles majors each, but they played doubles selectively and spent only eight weeks at No. 1 each. No one this century has spent more weeks at No. 1 than Siniaková.

She is the first player to complete the career Grand Slam with two different partners, one of only seven women with a Career Golden Slam and one of four with a Career Super Slam, and her Grand Slam win rate is about 81%. She has won majors with three different partners.

There is a strong case for arguing that Siniakova is the best doubles player of the 21st century based on her titles, longevity and versatility, while a place in the Open Era's top five is also defensible. Surpassing Fernández's 17 Grand Slam doubles titles would require six more majors, while overtaking Zvereva's 18 would take seven. Navratilova's record of 31, however, remains out of reach. Nevertheless, Siniakova's rankings and Olympic achievements already place her among the most accomplished all-around doubles players of the post-2000 era.

Siniakova's singles career is the part of her résumé that is easy to overlook. She has won five WTA titles, lifting trophies in Shenzhen and Bastad in 2017, Portoroz in 2022 after defeating Elena Rybakina, and Bad Homburg and Nanchang in 2023. She has also finished runner-up on five occasions. Her career-high ranking of No. 31 came in October 2018, and she has ended eight of the last 10 seasons inside the top 50.

The contrast between her two careers explains much of how she is perceived. In singles, Siniakova has been a consistent top-50 player, while in doubles she has established herself as the world's leading competitor.

Nevertheless, her singles achievements deserve recognition in their own right. She has recorded 12 victories over top-10 opponents, including Simona Halep, Serena Williams and Garbiñe Muguruza. Her most recent top-10 win came against defending champion Mirra Andreeva at Indian Wells earlier this year.

Her recent singles results, however, have been less encouraging. Siniakova has not recorded consecutive victories since June, and her early exit at the Wuhan Open leaves her ranked around No. 87, with a few weeks remaining in the season to improve her position. That would represent a significant drop from her usual year-end standing, given that she has finished eight of the last 10 seasons inside the top 50. Her lowest year-end ranking during that period was No. 64 in 2020.

Siniakova is 37 weeks away from matching Martina Navratilova's record for most weeks spent at world No. 1 in doubles, equivalent to roughly nine months. She is also one year-end No. 1 finish away from surpassing Navratilova's mark. Winning a 13th Grand Slam doubles title would further strengthen her position in the Open Era rankings, while the WTA Finals represent another major opportunity as the season approaches its conclusion.

It remains to be seen whether Siniakova will continue her partnership with Taylor Townsend or eventually seek another successful doubles combination. At 30, the Czech still has several years in which to extend her career, and her record makes her an attractive partner for players seeking Grand Slam success.

For now, the debate over the greatest doubles player of the 21st century has a clear leading candidate in Siniakova, whose career continues to add to an already exceptional résumé.