Reigning women's US Open champion Aryna Sabalenka advanced to the semi-finals on Tuesday when Marketa Vondrousova pulled out of their last-eight clash with a knee injury.

"I am sorry to announce that I have to withdraw from my quarter-final match this evening due to a knee injury," Vondrousova said in a statement.

"I tried my best to take the court today but during the warm-up I felt again my knee and after consultation with the tournament doctor decided not to risk aggravating the injury."

World number one Sabalenka plays fourth-seeded American Jessica Pegula in the last four Thursday in a repeat of last year's final won by the Belarusian.

"So sorry for Marketa after all she's been through. She has been playing amazing tennis and I know how badly this must hurt for her," Sabalenka wro

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