Serena Williams suffered a third set collapse against Karolina Pliskova. Pliskova won 6-4, 4-6, 7-5 .

After leading 5-1 in the final set, Wlliams’ game unraveled. She had four match points but couldn’t convert. Williams , it appeared, rolled her ankle, which affected her movement after she had landed awkwardly in a foot-fault on the first of four match points . Pliskova picked up her game from that point and William could not find hers.

“I did everything I could on those match points,” Williams said. “I can’t say that I choked. [Pliskova] literally played her best tennis ever on those shots. I’ve never seen anything like it. Next time I’m up 5-1 against anybody, I need to make sure I play lights out. It’s a good learning experience.”

“I just felt a chance,” Pliskova said of that moment. “For sure it was in her head. I saw a chance and I just took it.”

Pliskova next plays US Open champion Naomi Osaka, who easily beat Elina Svitolina 6-4, 6-1. In the other semifinal, American Danielle Collins plays Petra Kvitova.

World Number 1, Simona Halep was the underdog against Serena Williams. So it was not a surprise that Willilams won by a 6-1, 4-6, 6-4 score. But it wasn’t easy. Halep put up a good fight despite the one-sided first set. Williams will next play Karolína Pliskova, meanwhile, has won all nine matches she has played this season.

Williams’s is aiming for her 24th grand slam title, at last equaling the Australian great Margaret Court’s total of major singles championships.Her coach, Patrick Mouratoglou, offered the strongest assessment. “I believe she will,” he said. “She is ready physically, I think emotionally, too.” “She is back,” he added, “to being Serena.”

“I have to return better, but I will be ready,” Williams vowed as she looked ahead to Pliskova. “She’s ready, I’m ready, let’s do it.”