Isner forced out

John Isner pulled out of the Winston-Salem Open ahead of his quarter-final against Lukas Rosol due to a sprained ankle.

Isner, the world no 15, sustained the injury to his left ankle on Wednesday evening during his third-round victory over Mikhail Kukushkin.

And, with the US Open starting on August 25, the 6ft 10in American opted not to risk aggravating the problem and instead withdrew a few hours before he was due to meet Rosol.

Czech Rosol advances to a semi-final against ninth seed Yen-Hsun Lu of Taiwan, who saw off Italy's Andreas Seppi 6-4 6-4 in the last eight.