TORONTO, Canada (AFP) — World No. 2 Elena Rybakina came from a set down to defeat four-time Grand Slam winner Naomi Osaka on Tuesday and reach the WTA Toronto Masters semifinals, where she will face fourth-ranked Coco Gauff.

Rybakina, the reigning Australian Open champion from Kazakhstan, fired 13 aces in a 4-6, 7-6 (7/5), 6-4 victory.

“Super happy. It was a very difficult match,” Rybakina said after a tight battle lasting two hours and 33 minutes.

“In the first set (I made) a few mistakes, a poor start.”

“It was a really tough one but I’m glad I could turn it around, I don’t yet know how, but I think my serve helped me a little bit.”

Gauff, a 22-year-old American, had a walkover into her first Canada semi-final when Switzerland’s Belinda Bencic withdrew with a hip injury.

“I’m really sorry to not be able to compete,” Bencic said in a statement. “I tried everything possible to be ready. Looking forward to being back in Toronto next time.”

Gauff, the 2023 US Open and 2025 French Open champion, defeated Rybakina in their only previous meeting, which came at Toronto in a 2022 third-round match.

“She’s a fighter,” Rybakina said of Gauff.

“I definitely need to bring my energy and serve well.”

Poland’s Iga Swiatek and Ukraine’s Elina Svitolina meet in Wednesday’s other semi-final.

Osaka and Rybakina staged a dramatic duel in their first ever meeting on tour.

“We practiced a couple of times before so I more or less knew how the ball was going to come, what to expect,” Rybakina said.

“In some moments my energy wasn’t there but I’m glad in the end it went my way.”

Rybakina double-faulted to hand Osaka a break in the opening game and the Asian star held serve from there to claim the first set in 42 minutes.

The pair exchanged breaks of service twice in a drama-filled second set but in the tiebreak Rybakina never trailed and smashed a forehand winner to force a third set.