World number two Elena Rybakina rallied from a set down to beat four-time Grand Slam champion Naomi Osaka on Tuesday, advancing to 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 2 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 semifinal 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 semifinal. 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. "I was trying to stay close on the score, trying not to think if I make a mistake, just keep going," Rybakina said.
Osaka was denied on four break points in the sixth game as Rybakina held. The Kazakh broke for a 4-3 lead as Osaka missed a forehand smash wide on game point, then sent forehands long and wide. Rybakina sealed the match with a second-serve ace, winning all 18 of her first-serve points in the final set.
World number 13 Osaka, who took a break, has not won a title since the 2021 Australian Open. Rybakina is within touching distance of becoming world number one for the first time.
If the two-time Grand Slam champion wins the Toronto title, she would move to just four ranking points behind Aryna Sabalenka, who lost in the last 16.