Winston-Salem, NC (SportsNetwork.com) - Two-time champion John Isner pulled out of the Winston-Salem Open on Thursday, citing a sprained ankle.
Tournament organizers said the 6-foot-10 American injured his left ankle Wednesday night during his third-round victory over Kazakhstan's Mikhail Kukushkin.
The top-seeded Isner was scheduled to meet seventh-seeded Czech Lukas Rosol in the quarterfinals, but Rosol advanced via walkover at this final U.S. Open tune-up on the hardcourts at Wake Forest University.
Isner, who hails from nearby Greensboro, North Carolina, titled here back-to- back in 2011 and 2012.
Rosol's semifinal opponent will be ninth-seeded Taiwanese Yen-Hsun Lu, who handled 14th-seeded Italian Andreas Seppi 6-4, 6-4 on Day 5.
Another quarterfinal result saw 6-foot-8 Pole Jerzy Janowicz cool off Belgian David Goffin 6-4, 6-2. The qualifier Goffin had won his last 25 matches, including a recent ATP title in Austria and three Challenger Tour championships.