PARIS - Mob rule continued in the women's tournament of the French Open on Friday when Caroline Wozniacki, the world's No. 1 player, was upset in the third round, 6-1, 6-3, by Daniela Hantuchova.

The lopsided defeat will only increase debate about Wozniacki's worthiness for the top spot, and it came a day after Kim Clijsters, Wozniacki's closest pursuer in the rankings, was eliminated in the second round after losing her way against Arantxa Rus, the world's 114th-ranked player.

"Since we're No. 1 and No. 2, it means we must be doing something right; it's just unfortunate to lose in a Grand Slam," Wozniacki said.

This is the first time since the Open era began in 1968 that the Nos. 1 and 2 women's seeds have failed to reach the Round of 16 in a Grand Slam.

Earlier Friday, the No. 8 seed, Samantha Stosur, a big-hitting Australian who reached the final here last year, also lost, to Gisela Dulko of Argentina.

On the men's side, two-time Australian Open champion Novak Djokovic, who is on a 41-match winning streak, was tied at a set apiece with 2009 U.S. Open champion Juan Martin del Potro when play was suspended at 9:15 p.m. because of darkness.

The second-seeded Djokovic won the first set, 6-3, but No. 25 del Potro took the second by the same score. After del Potro held serve to even the match, the chair umpire said play would stop for the day; there are no artificial lights on the courts at Roland Garros.

Earlier, 16-time Grand Slam champion Roger Federer of Switzerland, the No. 3 seed, saved the only break point he faced in a 6-1, 6-4, 6-3 victory over No. 29 Janko Tipsarevic of Serbia.

The only member of the women's top four who has not struggled here is fourth-seeded Victoria Azarenka of Belarus, who, despite injuring her elbow this month, has dropped just seven games in her first two matches.

But Azarenka's good friend Wozniacki was nowhere near as effective against Hantuchova, a smooth-moving Slovakian veteran who once was ranked No. 5 but who is seeded 28th here this year.

"She played very, very well today, better than me, for sure," Wozniacki said. "She knew what she was going to go out there and do. She was just too good."

Wozniacki had not dropped a set against Hantuchova in their previous three matches, but she dropped the first in a hurry on the Suzanne Lenglen Court, the second biggest show court at Roland Garros and the scene of many major upsets.

Wozniacki then fell behind, 0-4, in the second set before rallying to 3-4. But Hantuchova, often shaky under pressure, recovered and finished off the victory, with Wozniacki making unforced errors on the final two points.

Clay is not Wozniacki's favorite surface. She grew up in Denmark playing mostly on hard courts.

This article contains information from the Associated Press.