Paris ? Venus Williams shanked overheads, dumped volleys into the net and had 70 unforced errors in all. Not at her best, it didn’t help that she was facing a younger version of herself in 17-year-old Nicole Vaidisova.

With power aplenty, Vaidisova reached her first Grand Slam semifinal by rallying to defeat Williams 6-7 (5), 6-1, 6-3 Tuesday at the French Open.

“You can believe I’ll watch the film and figure out the things I didn’t do right,” said Williams, a five-time major champion and former No. 1. “She deserved to win.”

Vaidisova knocked off the current No. 1, Amelie Mauresmo, in the previous round, and now will meet 2004 U.S. Open champ Svetlana Kuznetsova for a berth in Saturday’s final.

Kim Clijsters plays 2003 and 2005 French Open champion Justine Henin-Hardenne in an all-Belgian semifinal, and a win would push Clijsters back to No. 1 in the rankings.

The 16th-seeded Vaidisova is the only member of the women’s final four who hasn’t won a Grand Slam title. When she was a child, she played with the same yellow racket she’d seen Williams use. Two years ago, Vaidisova made her Grand Slam debut as a qualifier at the U.S. Open, and was excited to simply set foot in the locker room, gawking at the collection of tennis stars.

Germany's Anna-Lena Groenfeld eyes the ball in her French Open quarterfinal match against Belgium's Justine Henin-Hardenne on Tuesday in Paris. Henin-Hardenne won 7-5, 6-2.

Is she one of them now?

“No, not yet,” Vaidisova said, smiling, “but I’m working on it.”

Kuznetsova erased a 5-1 deficit in the first set against No. 14 Dinara Safina and won 24 of 27 points in the second en route to a 7-6 (5), 6-0 victory. Clijsters beat Martina Hingis 7-6 (5), 6-1, and Henin-Hardenne eliminated Anna-Lena Groenefeld 7-5, 6-2.

In the men’s quarterfinals, top-ranked Roger Federer beat No. 12 Mario Ancic 6-4, 6-3, 6-4 for his 26th consecutive victory in Grand Slam action His semifinal foe will be David Nalbandian, a 6-3, 6-3, 2-6, 6-4 winner over No. 6 Nikolay Davydenko.