Anastasija Sevastova stunned two-time defending champion Jessica Pegula 3-6, 6-4, 6-1 to book a fourth-round clash with Naomi Osaka at the WTA Canadian Open.

Sevastova, a former world No 11 now ranked 386th, snapped fourth-ranked Pegula's 11-match WTA Canada win streak, the longest since Serena Williams reeled off 14 consecutive wins in 2011, 2013 and 2014.

Pegula, last year's US Open runner-up in her best Slam showing, was the first woman to win back to back Canadian Open titles since Martina Hingis in 1999-2000. But she has struggled in recent months, dropping her openers at Wimbledon and at Washington last week.

Sevastova will try to extend her Montreal run in a round of 16 meeting with Osaka, a four-time Grand Slam champion from Japan who ousted another Latvian, 22nd seed Jelena Ostapenko, 6-2, 6-4.

Osaka, twice a winner at both the US and Australian Opens, is one match away from her first quarter-final run at either a Grand Slam or WTA 1000 event since she returned from maternity leave at the start of 2024.

"Somehow, I was down 2-0 in the second set and started to play better and better," Sevastova said. "Third set I played really good.

"Just trying to stay on the court as long as possible," added Sevastova who has dealt with injury since returning from maternity leave in February 2024.

In the night session, second-seeded Iga Swiatek – playing her first tournament since winning Wimbledon – raced into the fourth round with a 6-2, 6-2 victory over Germany's Eva Lys.

Swiatek next faces Denmark's Clara Tauson, who beat Yuliia Starodubtseva 6-3, 6-0.

Australian Open champion Madison Keys, seeded sixth, beat fellow American Caty McNally 2-6, 6-3, 6-3 and will next meet Karolina Muchova, a 6-7 (2/7), 6-2, 6-3 winner over Belinda Bencic. (AFP)