PARIS - One shot by Serena Williams sent Svetlana Kuznetsova to the court in a messy spill that left her covered with clay.

The Russian was down but not out. Showing newfound resilience, she squandered a big lead in the second set yesterday but ended Williams' 18-match Grand Slam winning streak in the French Open quarterfinals, 7-6 (3), 5-7, 7-5.

Williams, seeded second, was seeking her third successive major title and the 11th of her career.

Roger Federer moved one step closer to the only Grand Slam title he has yet to win, beating Frenchman Gael Monfils, 7-6 (6), 6-2, 6-4. It's the 20th consecutive time Federer has reached the semifinals in a major tournament.

Federer is 5-0 against his opponent tomorrow, No. 5-seeded Juan Martin del Potro. The 6-6 Argentine advanced to his first Grand Slam semifinal by beating No. 16 Tommy Robredo, 6-3, 6-4, 6-2.

Williams was on the verge of reaching the women's final four after mounting a comeback and taking a 3-1 lead in the final set. She blamed nerves for her defeat.

"In the third set I had an opportunity and I got really tight, and I pretty much gave it to her," Williams said. "It was like, 'Here, do you want to go to the semis? Because I don't.' She was like, 'OK.' "

The No. 7-seeded Kuznetsova faced a set point serving at 5-6 in the first set but erased it with a slam and took the lead. After Kuznetsova's tumble in the second set, Williams erased a 5-3 deficit and rallied three points from defeat to even the match.

"It was very confusing," Kuznetsova said. "Yes, I missed my moments, but she also was playing good."

Kuznetsova mounted the final surge and overcame her history of shaky play when trying to close out big matches. Instead it was Williams who succumbed to the tension.

Why the nerves?

"I don't know," Williams said. "I haven't gotten tight since 2007 in Australia. I maybe I put some expectations on myself that I didn't put on myself initially."

Williams won her only French Open title in 2002.

Kuznetsova, the 2004 U.S. Open champion, seeks her second major title. Her opponent today will be Samantha Stosur, 25, of Australia, who reached her first major semifinal by beating Sorana Cirstea of Romania, 6-1, 6-3.

Kuznetsova was serving one point from a 5-2 lead in the second set when she turned her right ankle in pursuit of a shot and fell on her back. She rose caked with clay - it was even in her hair and on her forehead.

She was unhurt and play quickly resumed, but it took a while for Kuznetsova to regain her footing. Later she could smile about the spill.

"See the sand?" she said at her postmatch news conference. "I still have clay in my hair."

Federer's path to a record-tying 14th Grand Slam title became easier when four-time defending champion Rafael Nadal was upset Sunday. With Nadal's absence comes higher expectations.

"I felt some pressure before this match," Federer said. "I was very nervous, because I thought it would be very difficult." *