MELBOURNE, Australia — The much-anticipated potential quarterfinal between the back-from-retirement Belgians dissolved in 52 minutes Friday at the Australian Open.

That's the time it took for Kim Clijsters to lose, in embarrassing fashion, her third-round match at the season's first Grand Slam tournament.

The 6-0, 6-1 defeat to Nadia Petrova was the worst of Clijsters' career and as one-sided as the score indicated. Clijsters lost the first set in just 18 minutes and won only five points in her first seven games.

Justine Henin, another Belgian who was inspired to return to the tour following a 20-month absence after Clijsters won the U.S. Open, held up her end of the bargain. With some difficulty, she defeated Alisa Kleybanova 3-6, 6-4, 6-2.

"I just didn't give her a chance to get into the match," Petrova said. "I like this kind of Grand Slam feeling."

Clijsters hadn't been on the receiving end of such a lopsided scoreline since losing the French Open final to Henin 6-0, 6-4 in 2003.

"I was completely off. I think tennis-wise, I didn't feel the ball at all," Clijsters said. "On the other hand, she was good, but I made all the mistakes and she really didn't have to do much.

"It's something you don't want to happen too often. It sucks that it has to happen at this stage of this tournament."

Defending champion Rafael Nadal advanced to the fourth round Friday along with Andy Murray, U.S. Open champion Juan Martin del Potro, Andy Roddick and Fernando Gonzalez.

Nadal, who beat Roger Federer in last year's final, held off Philipp Kohlschreiber of Germany 6-4, 6-2, 2-6, 7-5 in a night match.

In the fourth round, Nadal will play Ivo Karlovic, who beat Ivan Ljubicic 6-3, 3-6, 6-3, 7-6 (7). The 6-foot-10 Karlovic holds the tour record for the most aces in a match with 78.

"He's a really difficult opponent because the match is decided in a few points," Nadal said. "So the thing is to concentrate with my serve all the time and try to convert the small opportunities that I can have on the return."

The fifth-seeded Murray, bidding to win his first Grand Slam singles title, beat Florent Serra of France 7-5, 6-1, 6-4 and is one victory away from a potential quarterfinal with Nadal.

First, Murray will have to beat American John Isner, who won at Auckland last week for his first ATP title. The 6-foot-9 Isner continued his strong play by defeating 12th-seeded Gael Monfils of France 6-1, 4-6, 7-6 (4), 7-6 (5).

"I was just kind of riding a wave of momentum, and I still am," Isner said. "Hopefully, I can keep it going."

No. 4 Del Potro beat Florian Mayer of Germany 6-3, 0-6, 6-4, 7-5 and No. 7 Roddick advanced 6-7 (4), 6-4, 6-4, 7-6 (3) over Feliciano Lopez of Spain.

Next up for del Potro is Marin Cilic, who stopped Stanislas Wawrinka 4-6, 6-4, 6-3, 6-3.

Gonzalez, the 2007 finalist, beat Evgeny Korolev of Kazakhstan 6-7 (5), 6-3, 1-6, 6-3, 6-4. Roddick and Gonzalez will play each other in the fourth round.

Gonzalez was supported Friday by a throng of noisy, flag-waving Chilean fans on Show Court 2. Roddick is wary of his next opponent, despite holding an 8-3 edge in career meetings and a straight-sets win the last time they met at the 2008 U.S. Open.

"He's a very dangerous player," the 2003 U.S. Open champion said. "Some days he comes out, looks like he's playing Ping Pong the way he can sling the ball around. I don't think there are going to be a lot of secrets out there."

Henin's match Friday was her eighth since she returned from retirement, just long enough to expect better of herself as a seven-time Grand Slam singles champion.

She let that show Friday. After fluffing a routine volley to set up two break points for her opponent, she picked up the ball with her racket, bounced it into her left hand and threw it over the net in disgust.

The minor tantrum seemed to work. Minutes later, a point away from trailing 4-1 in the second set Henin rallied instead to even it. From then, she dominated the match.

Henin will play Yanina Wickmayer in the fourth round.

Wickmayer is ranked No. 16 but unseeded because she was under a suspension — since overturned — for breaching the World Anti-Doping Agency's "whereabouts rule." She advanced 6-1, 6-7 (4), 6-3 against Sara Errani.

Wickmayer received treatment on her back during the second set and hopes the injury will not be a problem for Henin's match.

"Let's hope I can fix it up by the next match," she said. "It will be a question."

Second-seeded Dinara Safina, the 2009 finalist, advanced with a 6-1, 6-2 victory over Britain's Elena Baltacha.

Next she faces fellow Russian Maria Kirilenko, who beat Italian Roberta Vinci 7-5, 7-6 (4). Kirilenko ousted 2008 champion Maria Sharapova in the opening round.

"I think Sharapova hits it harder than Safina, so I am prepared," Kirilenko said.

French Open champion Svetlana Kuznetsova struggled but advanced in a night match, beating 118th-ranked Angelique Kerber of Germany 3-6, 7-5, 6-4.

Former No. 1 Jelena Jankovic was upset 6-2, 6-3 by No. 31 Alona Bondarenko.

Three-time Australian champion Federer, 2008 winner Novak Djokovic, defending women's champion Serena Williams and her sister, Venus, play third-round matches.