PARIS — Serena Williams, of all people, got a case of the jitters.

That was her explanation, anyway.

The 10-time Grand Slam champion kept finding herself in, then out of, trouble in the French Open quarterfinals yesterday, until running out of stamina and strokes down the stretch of a 7-6 (3), 5-7, 7-5 loss to Svetlana Kuznetsova that ended Williams' 18-match winning streak at major tournaments.

"I had an opportunity, and I got really tight, and I pretty much gave it to her," said the second-seeded Williams, who blew a 3-1 lead in the third set. "It was like, 'Here. Do you want to go to the semis? Because I don't.' She was like, 'OK.' "

The seventh-seeded Kuznetsova's semifinal opponent today is No. 30 Samantha Stosur of Australia, who defeated Sorana Cirstea of Romania, 6-1, 6-3. The other women's semifinal is No. 1 Dinara Safina of Russia against No. 20 Dominika Cibulkova of Slovakia.

If Stosur-Cirstea was as onesided as could be, Kuznetsova-Williams was hyper-competitive and superbly played. Until, at least, Kuznetsova (kooz-NET-so-vah) took eight of the last nine points, breaking Williams in the final game.

"Honestly, I think I lost because of me," Williams said, "and not because of anything she did."

Williams denied she felt fatigued, blaming nerves instead.

How could that be?

"Maybe I put some expectations on myself that I didn't put on myself initially," she said.

With Williams, the 2002 French Open champion gone, Kuznetsova, the 2004 U.S. Open champion, is the only member of the remaining quartet to have won a major title. Neither Stosur nor Cibulkova has won any singles title on tour.

Stosur, a 25-year-old Australian, dominated for the second straight match on center court to reach the semifinals at a major tournament for the first time.

"Doesn't matter who you are, everyone knows that it can be effective," Stosur said of her serve. "It certainly works here and on hard courts, anything where it is going to bounce high."

In the fourth round, Stosur easily beat Virginie Razzano, 6-1, 6-2. The Frenchwoman then paid Stosur a compliment, saying, "She serves like a man."

Against Cirstea, Stosur won 92 percent of the points on her first serve in the first set. In the second, Stosur saved eight of the nine break points she faced.

"I'm just really pleased that even though I may have been down in the game, I could hang in there and fight my way back," Stosur said. "If she was going to win the game she had to earn it from me. I wasn't going to give anything away today."