Serena Williams’ coach blames US Open loss on hurt knee

Serena Williams of the United States reacts against Karolina Pliskova of the Czech Republic during her Women's Singles Semifinal Match on Day Eleven of the 2016 US Open at the USTA Billie Jean King National Tennis Center on Thursday in the Flushing neighborhood of the Queens borough of New York City.  (Photo by Elsa/Getty Images)

Serena Williams of the United States reacts against Karolina Pliskova of the Czech Republic during her Women's Singles Semifinal Match on Day Eleven of the 2016 US Open at the USTA Billie Jean King National Tennis Center on Thursday in the Flushing neighborhood of the Queens borough of New York City. (Photo by Elsa/Getty Images)

NEW YORK – Serena Williams’ coach is blaming her U.S. Open loss squarely on her injured left knee.

Patrick Mouratoglou said after the straight-set semifinal upset by Karolina Pliskova on Thursday: “It’s impossible to compete without moving. That’s why she missed so much, so many unforced errors, was because she was so slow.”

Williams said later that the injury’s effect was more mental than physical. Mouratoglou insisted that if Williams had been “20 percent less injured, she would have won in two sets.”

Player and coach also differed on when Williams was initially hurt. He said it was a new injury that occurred late in her quarterfinal, while she said it first bothered her earlier in the tournament.

According to Mouratoglou, Williams received treatment all day and scrapped most of her warm-up.

“With the adrenaline of the match, we never know. But since the start it was terrible,” he said. “At the end she tried to go for the winner on every shot. Even if she wins the second, it’s not the point. She’s not going to win the third.”