Elena Rybakina, the 2022 Wimbledon champion, and Canadian teen Victoria Mboko advanced to a WTA Canadian Open semifinal matchup with triumphs on Monday in the Montreal hard court event.
World number 12 Rybakina of Kazakhstan led 6-1, 2-1 when Ukraine's Marta Kostyuk retired in the second set with a wrist injury.
Mboko, the shocker of the event, dispatched Spain's Jessica Bouzas Maneiro 6-4, 6-2 by taking the final six games to reach her first WTA 1000 semifinal in pursuit of her first trip to a WTA final.
"I'm so excited to be in the semifinal here," Mboko told the supportive home nation crowd. "I want to thank everyone for your support once again. It has been unreal."
Rybakina won their only prior meeting 6-3, 7-5 last month in the second round at Washington.
The top five seeds and seven of the top 10 seeds were ousted before the quarterfinals, opening the door for such upstarts as 18-year-old Mboko, who eliminated top seed Coco Gauff.
World number 85 Mboko, who began the year raked 333rd in the world, has ensured herself a jump into the top 50 for the first time in her career next week.
Mboko broke 51st-ranked Bouzas Maneiro for a 5-3 lead. The Spaniard broke back in the ninth game only to drop the first set after 43 minutes when Mboko broke again.
Bouzas Maneiro broke to open the second set then held but Mboko never dropped a game from there, taking the match after 77 minutes when the Spaniard sent a backhand beyond the baseline.
The crowd, which chanted "it's not over" in French after the match, has been the best part of the amazing run, Mboko said.
"I train here (in Canada) and it's always a great opportunity to be here," Mboko said. "My first time playing in Montreal has been an unreal experience and I couldn't be more grateful."
Rybakina, seeded ninth, seeks her third WTA title after Rome and Indian Wells in 2023. She has not reached a final since last year at Miami.
Rybakina broke 24th-seeded Kostyuk to open the match and led 2-1 when Kostyuk received medical treatment on her right wrist and forearm.
Kostyuk netted a backhand to surrender a break in the fifth game and Rybakina broke again to claim the first set in 37 minutes when Kostyuk sent a forehand long.
In the second set, Rybakina held twice before Kostyuk retired after 54 minutes due to her wrist issues, walking off the court in tears.
Tuesday's quarterfinal matches send four-time Grand Slam champion Naomi Osaka of Japan against Ukraine's 10th-seeded Elina Svitolina and US sixth seed Madison Keys, this year's Australian Open champion, against Danish 16th seed Clara Tauson.