NEW YORK—Four questions into her press conference that followed her stunning US Open semifinal loss, Serena Williams was already weary of a tired topic.

Williams shot down suggestions fatigue from her two hour, 14-minute quarterfinal conquest of Simona Halep played a part in her 6-2, 7-6 (5) loss to 10th-seeded Karolina Pliskova.

US Open: Pliskova Stuns Serena

Twenty-one hours after beating Halep, Williams took the court against Pliskova, who is 10 years her junior.

The top seed, who double faulted on match point, said fatigue was not a factor in her second straight US Open semifinal exit.

"Okay, I'm not going to repeat myself. I wasn't tired from yesterday's match," Williams said. "I'm a professional player; been playing for over 20 years. If I can't turn around after 24 hours and play again then I shouldn't be on tour. So I definitely wasn't tired from yesterday's match at all.

"It wasn't a five-hour match. I have practiced three hours, so it wasn't that huge of a deal."

Williams, whose Open Era record-tying streak of 186 straight weeks as world No. 1 came to an end with the defeat, said a left knee injury she suffered in the second or third round hindered her movement.

"I have been having some serious left knee problems," Williams said. "I wasn't tired. Fatigue had absolutely nothing to do with it. If I was tired I should definitely get into a new career.

"I wasn't able to move the way I wanted to move. When you're injured you're thinking of other things when you should be just playing and thinking of your shots. My mind was just a little bit everywhere. But it was what it was."

Asked about 28-year-old Angelique Kerber succeeding her as world No. 1, Williams replied: "I'm not talking about No. 1. Thank you."

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