Elena Rybakina stunned Iga Swiatek to confirm her place in the knockout stages of the WTA Finals, while Amanda Anisimova produced a comeback victory to stay in contention in Riyadh.

Former Wimbledon champion Rybakina was outplayed in the opening set against world number two Swiatek but completely dominated thereafter.

Sixth seed Rybakina won 12 of the final 13 games to storm to a 3-6 6-1 6-0 win and snap a four-match losing streak against Swiatek.

American Anisimova later beat Madison Keys to send Rybakina through to the semi-finals.

"Mentally, I am happy that I stayed focused. I got some confidence in the second set and everything was going my way," Rybakina said.

"Hopefully, I will play like that through the whole tournament."

Anisimova battled back from a set and a break down to beat compatriot Keys 4-6 6-3 6-2 and set up a winner-takes-all final group match against Poland's Swiatek on Wednesday.

Wimbledon and US Open runner-up Anisimova, appearing at her first Finals, let out a roar of frustration after going 2-0 down in the second set but recovered superbly to win 12 of the next 15 games.

Keys did not shake hands with Anisimova at the end of the match, explaining to her opponent that she was ill.

The leading eight women's players in singles and doubles are competing in Saudi Arabia, where £12m ($15.5m) in prize money will be won.

Rybakina ends wait for Swiatek win

Rybakina was backed to challenge Aryna Sabalenka and Swiatek for the sport's top prizes after her Wimbledon triumph in 2022.

But, while the world's current top two have won eight of the 13 slams since then, the 26-year-old Kazakh has been unable to build on that breakout success.

Swiatek had won all four of her previous meetings with Rybakina in 2025, losing only one set in the process, and leads the WTA Tour for match wins this year (62).

But, despite a positive start, an overwhelmed Swiatek had no answer once the momentum shifted, with this her first loss after winning the first set since January's Australian Open.

Rybakina, who only secured her spot at the year-end championships two weeks ago, responded emphatically after Swiatek edged the opening set with an early break of serve.

The tour leader for total aces in 2025 (480), the big-hitting Rybakina found rhythm on serve and forced Swiatek to play deep behind the baseline, while Swiatek's own first serve points won fell from 90% in the first set to 53% in the second.

A double break of serve ensured Rybakina swiftly restored parity - and the outcome never appeared in doubt after she rallied from 40-15 down to break Swiatek at the start of the final set.

A fading Swiatek was powerless to halt her opponent's progress as she amassed 42 unforced errors - 36 of which came in sets two and three - compared to just 12 winners.

Rybakina completed a statement first win over Swiatek for 19 months with a second serve ace to extend her winning run to eight matches.

The one-sided conclusion also made Swiatek the first player to suffer a 6-0 third-set scoreline in three matches in a season since 2013.

In the doubles competition, Taiwan's Hsieh Su-wei and Latvia's Jelena Ostapenko confirmed their place in the knockout stage with a 6-3 6-4 win against Italian top seeds Sara Errani and Jasmine Paolini.

Elise Mertens and Veronika Kudermetova then eliminated Asia Muhammad and Demi Schuurs with a 6-4 6-7 (6-8) 10-6 win.