Sebastian Korda had a rough end to a good day at the Winston-Salem Open on Thursday in North Carolina.

The third-seeded U.S. player defeated 12th-seeded Richard Gasquet of France 4-6, 6-1, 7-6 (7) to reach the semifinals, but Korda withdraw from the event after the victory due to an ankle injury.

Korda said the injury occurred in the third set.

“Tough decision to pull out,” said Korda, who is looking ahead to the U.S. Open, which starts Monday in New York. “The ankle wasn’t getting any better. Hopefully it gets better the next couple days. Definitely a tough decision but I think a necessary one.”

Korda’s exit sends fifth-seeded Jiri Lehecka of the Czech Republic through to the Winston-Salem finale. Lehecka beat Australia’s Max Purcell 7-6 (4), 6-4 on Thursday.

The other semifinal will feature top-seeded Borna Coric of Croatia and sixth-seeded Sebastian Baez of Argentina, who both won rain-delayed quarterfinals Thursday night. Coric routed Argentina’s Juan Manuel Cerundolo, and Baez cruised past fourth-seeded Laslo Djere of Serbia 6-3, 6-0.

–Field Level Media