The champion is gone, and for Lindsay Davenport, the path to the finals could not look better.

In a stunning upset last night, Russia’s Nadia Petrova dethroned top-seed and defending champion Justin Henin-Hardenne in straight sets, 6-3, 6-2, punctuating her performance with an ace to seal the match.

Henin-Hardenne, the Olympic gold medalist, played sloppy from the start and framed shots that she normally strokes with ease, finishing with 30 unforced errors. She missed passing shots, could not find the court with her first serve and won only 10 of 30 points on her second serve.

Petrova, who had lost to Henin-Hardenne in each of their five previous meetings, joins two fellow Russians in the quarterfinals. She’ll play one of them, Svetlana Kuznetsova, on Wednesday. “I’m very satisfied with myself,” she said after her victory. “At the moment Russian tennis is doing so well.”

Henin-Hardenne, who has a reputation for toughness and knack for adjusting her versatile game at a moment’s notice, was stuck in a rut against Petrova. She said she was nervous and unable to change her tactics as the match progressed.

“It wasn’t my day,” she said. “She took the opportunities and it was very hard for me. I was very nervous and I couldn’t come through.”

The loss marked the first time since 1973 that a no. 1 seeded woman had lost in the round of sixteen or before at the U.S. Open. Billie Jean King was the last to do it.

Before Henin-Hardenne fell, Davenport cruised to victory over Venus Williams,7-5,6-4.If not for an intense final game that included five match points, scorching passing shots, and a few nerv ous mistakes, her impressive win would have had all the drama of a second-round win over an unseeded player.

The two stars were playing each other for the 25th time, and this time Davenport rolled over Williams, outplaying her from the baseline and firing big serves when she needed them most. It was her third straight victory over Williams this summer, and her 22nd straight victory overall since she lost in the Wimbledon semifinals to eventual champion Maria Sharapova. The win put her on a clear path to the semifinals against the winner of Petrova and Kuznetsova.

For fans expecting a tense all-American match, the last game, though not the best tennis, was worth the price of admission. It included 23 points and nine deuces. On her second match point, Davenport double-faulted. On her fourth, Williams stretched to return a big serve and then struck a forehand cross-court passing shot on the line as Davenport approached the net. In the end, Davenport had to stave off five break points before she belted a 102 mph service winner on match point. She pumped her fist and let out a squeal as she walked to the net toward a disappointed Williams.

“You know, it probably should have been five all,” said Davenport, who has now won 13 of her meetings with Williams. “It wasn’t a good game necessarily because the tennis was great. It was dramatic, I’ll say that.”

Davenport’s tennis may have been loose in the closing moments, but Williams played erratically throughout. She made 42 unforced errors as Davenport pounded the ball to her forehand time and again. Her serve failed her at important moments, too, including a double-fault to fall behind love 40 in the fifth game of the second set. Davenport won the game at love after Williams made an unforced error, and she held her serve the rest of the way.

Williams, who has struggled with nagging injuries this year, has not been her dominant self for quite some time. She still hits the ball as hard as anyone on the tour, but her mistakes have cost her big matches and a place in the top ten. As Davenport put it, “It’s easier playing her now than three years ago when they were all going in.”

Williams said her game has not recovered from all the time she has spent away from the practice courts. Whenever she got into a rally yesterday, Davenport seemed content to wait it out. Williams, she guessed, would make a mistake. “I felt like her errors were going to come back,” Davenport said. “If she can come up with a bunch of winners, that’s too good. But I was banking on the other happening.”

“I think in general I missed too much,” Williams said. She said that with more time on the court, she expected more of her shots to fall. “Next time, I’m going to have 10 less errors, I’m going to have 20 less errors.”

Davenport’s next opponent is the only unseeded player remaining in the women’s draw, Shinobu Asagoe of Japan. Asagoe continued her impressive run yesterday with a 7-6(4), 4-6, 6-3 victory over Greece’s Eleni Danilidou. Asagoe has lost to Davenport both times they have met.

“I’m not overreacting with the result that I have now because I’ll have another match they day after tomorrow,” Asagoe said. “But still I’m happy.”

Also yesterday, Mary Pierce, who defeated Maria Sharapova over the weekend, could not handle Kuznetsova, who dominated their match in straight sets, 7-6(5), 6-2. Kuznetsova hit 40 winners and 13 aces.

In doubles action, Martina Navratilova won two matches yesterday. In the afternoon, she and Lisa Raymond advanced in the women’s doubles, and then at night she and mixed doubles partner Leander Paes defeated Sharapova and Max Mirnyi in straight sets.