MELBOURNE, Australia — Martina Hingis has quickly quieted her doubters.

The former No. 1 player in the world, coming back from a three-year retirement, cruised past her third consecutive opponent Saturday to advance to the fourth round of the Australian Open on a day that the heat was some players' worst opponent.

Though there were questions about Hingis' fitness coming into the tournament, she looked fresh as she took the court for a late-morning match. She committed only 12 unforced errors in a 6-4, 6-1 victory in 65 minutes over Iveta Benesova, who suffered as temperatures rose.

"It wasn't as cruel, brutal" as later in the day, Hingis said. "Towards the end of the second set you could feel the heat, but thank God she felt it more than I did."

Hingis now has dropped only 10 games in her three matches and has looked almost as dominating as when she won three of her five Grand Slams here.

"I don't think I played my best tennis today," she said. "But as long as you win, it's always good. Always room to improve for the next match."

That will be against unseeded Australian Samantha Stosur, with a possible quarterfinal match looming against second-seeded Kim Clijsters.

Clijsters beat Italy's Roberta Vinci 6-1, 6-2 in 44 minutes, showing no obvious signs of the hip and back problems that have bothered her the last 10 days.

For the second consecutive day, the tournament invoked the extreme heat policy that calls for play to be suspended on outside courts after matches already under way were completed. The roofs were closed on Rod Laver Arena and Margaret Court Arena.

Temperatures exceeded 104 degrees — and were higher on court. Sunday's forecast calls for even hotter conditions before a cooler change next week.

Third-seeded Amelie Mauresmo was leading Michaella Krajicek 6-2 when the 17-year-old Dutch player withdrew because of heat stress.

Krajicek, with icebags around her neck, had her temperature and pulse taken by trainers before telling the umpire, "I can't play."

"I felt like I was going to throw up ... I couldn't even see the ball because my eyes were burning," Krajicek said after having an ice bath to cool down.

One player who wasn't complaining was 12th-seeded Dominik Hrbaty. He won his third consecutive five-set match, rallying from an 0-3 deficit in the fifth against No. 23 Igor Andreev of Russia.

Hrbaty, who already has spent 10½ hours on court, figured that his fitness — and his pink-and-black shirt that has come under ridicule with the two cutout holes in the back for ventilation — made the difference in his 3½-hour victory.

"I was tired already going to the match," he said. "If we would play inside, I think I wouldn't win with Andreev. I think it's more mental, how much you will be able to push yourself. And I feel like, 'Always never give up.' "

Hrbaty next faces fifth-seeded Nikolay Davydenko, who ousted the last Australian men's hope Nathan Healey 6-2, 5-7, 6-4, 7-5.

Also advancing were No. 25 Sebastien Grosjean — who needed almost 3 hours to upset No. 6 Guillermo Coria — No. 21 Nicolas Kiefer, Tommy Haas, Paul-Henri Mathieu and Argentina's Juan Ignacio Chela — who ousted No. 3 Lleyton Hewitt in the second round.

Chela appeared to be struggling in the third set, shuffling around slowly and frequently toweling off.

"Each point was an enormous effort," Chela said. "It was too hot. But it was the same for both players."

Advancing on the women's side were No. 7 Patty Schnyder, No. 12 Anastasia Myskina, the 2004 French Open champion, No. 16 Nicole Vaidisova and No. 15 Francesca Schiavone, who scored the tournament's first 6-0, 6-0 win — against Maria Sanchez Lorenzo in just 42 minutes.

Playing as a wild card and ranked No. 349, Hingis overwhelmed Benesova by mixing heavy ground strokes with clever slice and angled drop shots. She even had three aces.

Hingis won the first of her three consecutive Australian Open titles in 1997. The 25-year-old Swiss star lost finals from 2000-02 and quit the tour later that season. She returned on the Gold Coast earlier this month.

With every win comes increasing expectations.

"Coming into this tournament, I was like, 'OK, tough first round, see if I survive that one first,'" she said. "But one by one ... expectations definitely grow. With every match I'm getting more confidence."

Benesova, who said she felt dizzy from the heat in the second set, praised Hingis' savvy.

"She made me feel so uncomfortable because she's very clever; very smart player," Benesova said. "She knows exactly where to put the ball. It's like I had no rhythm.

"It's really amazing, after three years, not playing a match, and she's really mentally strong. She believes in her game. She knows what to do out there."

Roger Federer, the overwhelming favorite in the men's draw, was to face Max Mirnyi later Saturday.