Elena Rybakina stops playing during first set of quarterfinal vs. Iga Swiatek at Cincinnati

MASON, Ohio (AP) 鈥� Elena Rybakina stopped playing during the first set of her quarterfinal match against Iga Swiatek at the Cincinnati Open on Thursday night.

With the No. 2-ranked Rybakina serving at 1-4, 40-40, she took a medical timeout to have trainers address her left ankle area and retired from the match moments later.

鈥淥f course I feel not the greatest,鈥� Rybakina said. 鈥淚t’s painful to walk. We’ll know more tomorrow when we have the MRI. It’s been bothering me for a long period of time but felt like I had it under control.鈥�

After aggravating the injury during the second set on Thursday, she spent several minutes speaking with trainers before returning to the court. She decided to call it quits after she was unable to put full weight on her leg while attempting a serve.

鈥淚t was feeling OK before (Thursday鈥檚) match,鈥� Rybakina said. 鈥淯nfortunately one wrong movement and something happened.鈥�

With top seed Aryna Sabalenka losing Thursday night to Sara Bejlik, the 27-year-old Rybakina could have risen to No. 1 in the rankings by reaching the final.

Swiatek, the defending champion, has reached at least the semifinals in each of her last four appearances in Cincinnati. Swiatek beat Rybakina in the semifinals in Cincinnati last year. She’ll face American Jessica Pegula in the semifinals.

鈥淣ot the way you want the match to end,鈥� Swiatek said. 鈥淪he didn’t look good, obviously. Then she wanted treatment and I wasn’t sure if she was going to be back or not. She’s walking normally now. I felt really sorry for her but hopefully it’s nothing serious and she’s going to be ready for the U.S. Open.鈥�

Pegula beat fellow American Amanda Anisimova, 6-4, 2-6, 7-6 (4), on Thursday for her tour-leading 44th win of the season. It’s her second trip to the semifinals in Cincinnati; she lost to Sabalenka in the final two years ago.

Four American men reached the quarterfinals in Cincinnati for the first time since 1995, but Flavio Cobolli knocked out Tommy Paul on Thursday, 2-6, 6-3, 6-4, to reach his fifth semifinal this year and rise to a career-best No. 6 in the rankings. Cobolli is the second Italian man to reach the semis in Cincinnati, joining Jannik Sinner.

Cobolli will face 22-year-old Arthur Fils in the semifinals. Fils beat Thiago Agust铆n Tirante, 6-3, 6-2, to become the sixth man born since 2000 to reach three ATP Masters 1000 semifinals.

___