PARIS - Serena Williams 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 pits No. 1 Dinara Safina of Russia against No. 20 Dominika Cibulkova of Slovakia.

Roger Federer spoke about dealing with nerves yesterday, too, although his problems came before he began playing 11th-seeded Gael Monfils of France.

"We're all nervous at this stage of the competition. I felt it. Yesterday, I felt it, and I felt it again today in the warm-up," said Federer, who is in pursuit of the only Grand Slam tournament missing from his resume. "I was tired, I was nervous, and I didn't feel really good. Then once out on court, you know, I get my act together."

There's an understatement.

Federer beat Monfils, 7-6 (6), 6-2, 6-4, to close in on completing a career Grand Slam and earning a 14th major title to tie Pete Sampras' career record.

Next up for Federer is No. 5 Juan Martin del Potro of Argentina, who eliminated No. 16 Tommy Robredo in straight sets. Today's other men's semifinal will be No. 23 Robin Soderling - the man who upset four-time defending champion Rafael Nadal in the fourth round - against No. 12 Fernando Gonzalez.

Federer is 26-1 against the other semifinalists, including 5-0 against del Potro.

"Doesn't mean because I have a great record against all the players left in the draw that, you know, I'm going to win this,"

Federer said, "but I'll definitely try everything I possibly can to do it."

He is into his 20th consecutive major semifinal, extending his own record; del Potro is in the first of his career.

"We all know how he plays," the 20-year-old del Potro said.

The women's semifinalists might very well be relieved to know that 2002 French Open champion Williams is gone, because she was by far the most accomplished of the remaining players.

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.

Results

Seedings in parentheses.

MEN'S SINGLES

Men's quarterfinals: Roger Federer (2), Switzerland, def. Gael Monfils (11), France, 7-6 (6), 6-2, 6-4. Juan Martin del Potro (5), Argentina, def. Tommy Robredo (16), Spain, 6-3, 6-4, 6-2.

WOMEN'S SINGLES

Quarterfinals: Samantha Stosur (30), Australia, def. Sorana Cirstea, Romania, 6-1, 6-3. Svetlana Kuznetsova (7), Russia, def. Serena Williams (2), United States, 7-6 (3), 5-7, 7-5.

WOMEN'S DOUBLES

Semifinals: Anabel Medina Garrigues and Virginia Ruano Pascual (3), Spain, def. Cara Black, Zimbabwe, and Liezel Huber (1), United States, 7-5, 5-7, 6-2. Victoria Azarenka, Belarus, and Elena Vesnina (12), Russia, def. Hsieh Su-wei, Taiwan, and Peng Shuai (9), China, 6-3, 7-5.