No wonder, after being thoroughly beaten by the Czech player in the semifinals, she didn't feel quite like herself.
“I wasn't Serena today,” the top-ranked American said after a 6-2, 6-3 loss ended her 27-match WTA tour win streak dating back to 2014. “I'm just exhausted today.”
It was Kvitova's first win over Williams in six career meetings, but she dominated throughout with her powerful groundstrokes and broke the American six times.
“I had never beaten her, so it's a really special moment for me,” the two-time Wimbledon champion said.
In the men's tournament, Rafael Nadal advanced to the semifinals by beating Grigor Dimitrov, 6-3, 6-4.
“It's great news to be in the semifinals, it's a very positive result for me,” Nadal said. “I am pleased with the way I played this afternoon, very happy.”
Earlier, Kuznetsova beat Sharapova for the first time in seven years, breaking her opponent's serve three times and saving the one break point she faced.
Sharapova, who could have returned to No. 2 in the rankings with a victory, said she wasn't able to take advantage of Kuznetsova's second serves like she had done in the past.
“Today she had much more pop on her ball than I did, while I felt my shots were a bit too flat,” Sharapova said. “I also think the court and the bounce, with the altitude here, meant her spin was getting really high.”
Kuznetsova, who will be playing in her first final in nine months, is 1-3 against Kvitova but beat the Czech on clay last year at the French Open in their last meeting.