Iga Świątek advanced to the Cincinnati Open semi-finals on Thursday as world number two Elena Rybakina was forced to retire due to injury. The Kazakh player retired in the first set with an ankle problem in a setback to her preparations for the US Open Grand Slam, which begins on August 30. Świątek raced into a 3-0 lead before Rybakina got on the board, but the Kazakh was unable to halt Swiatek's momentum and called for a medical timeout before ending the match. The pair had also met in last week's Toronto final, where Świątek beat Rybakina in straight sets to claim the Canadian Open title. "I hope Elena will be fine, and obviously the next tournament is the priority," said Świątek, who extended her winning run to 10 matches. "I know this one is important as well, but the US Open is the US Open, and I hope she'll be ready for it. I thought we were playing a good game, but health is a priority." In another quarterfinal, American Pegula saw off her compatriot Amanda Anisimova 6-4 2-6 7-6(4) to set up a meeting with Świątek.