MELBOURNE, Australia — Outplayed from the start, defending champion Serena Williams was beaten by Slovakia's Daniela Hantuchova 6-1, 7-6 (5) in the third round of the Australian Open on Friday.

Williams struggled with her form in her first two matches, overcoming a number of errors to get by two low-ranked opponents. But Hantuchova, seeded 17th, took advantage of Williams' inconsistent ground strokes and kept her on the move from sideline to sideline.

Hantuchova clinched it on her fifth match point when Williams hit a return wide.

Williams waved to the crowd as she walked off court, wiping her face and neck with a towel.

"I was really set and very ready to play — I just made a lot of errors," Williams said. "I couldn't find my shots at all. I just didn't find my game. I was hitting balls every which direction."

Williams finished with 37 unforced errors and only 17 winners.

While showing flashes of the brilliance that earned her seven Grand Slam titles, Williams never got into a groove against the 22-year-old Hantuchova, who has never made it past the quarterfinals of a major and next faces No. 4 Maria Sharapova.

"I always believe in myself, the way to get there is to keep working hard, keep fighting for every point," said Hantuchova, adding that she'd play the same way in the next round. "I've got nothing to lose,"

Hantuchova, seen as a rising star since turning pro at age 16 in 1999, finally lived up to the high expectations. She said she had been her own worst enemy.

"I was not fighting myself at all as I used to," she said. "I had so many matches like this where I was really close to beating the top players and finally I did it today."

She also felt that Williams wasn't at her best.

"I think we all know how well she can really play," Hantuchova said. "But to her credit, I thought she kept fighting till the end."

Williams' loss means there will be no repeat singles champion at the Australian Open. Marat Safin, last year's men's winner, didn't make it to Melbourne due to injury.

The night match started with the roof open on Rod Laver Arena after a storm came through and cooled temperatures, which reached 96-plus degrees and caused tournament officials to shut the roof earlier in the afternoon.

Hantuchova broke quickly for a 3-1 lead before heavy rain swept through again, with Williams serving at 15-30.

With Williams unable to gather herself during the respite — and complaining that the court was still a little slippery after workers toweled off the surface — Hantuchova ripped through the rest of the set quickly, finishing off the set with her third service break.

Williams double faulted on the fourth deuce, and Hantuchova whacked a stinging forehand crosscourt service winner that Williams could only watch.

It was the first time Hantuchova had even taken a set from Williams, who easily won their three previous meetings.

Williams got an early break in the second set only to see Hantuchova break back to tie at 4-4.

After Hantuchova held for 6-5, Williams faced triple match point at 0-40, but saved all three with a swinging forehand winner, a shot on the line deep to Hantuchova's backhand that the Slovak hit wide and an ace.

Williams saved one more match point at 4-6 in the tiebreaker when Hantuchova hit a backhand wide. But Hantuchova finished it with a strong first serve that Williams weakly hit wide.

The cool conditions contrasted the heat on center court earlier in the afternoon.

After winning 17 of the first 18 points, second-seeded Andy Roddick zipped past frustrated Julien Benneteau 6-1, 6-2, 6-2 under a scorching sun. He will next face Marcos Baghdatis of Cyprus.

"On days like today where it is pretty hot, you just try to get through," Roddick said after smashing 17 aces, including three in the final game to finish in 1 hour, 22 minutes.

It was a day better suited to hitting the beach than hitting tennis balls. Bags of ice dangled around players' necks or draped across their thighs. Shade was a precious commodity.

The extreme heat policy was put in effect when the temperature exceeded 96. New matches on outside courts were suspended under the so-called heat stress index guideline, which combines the ambient air temperature and court surface temperature. Five matches were postponed when a late storm came through.

Top-seeded Lindsay Davenport struggled in the heat, hitting 42 unforced errors.

"It was a lot hotter than I anticipated it was going to be," said Davenport, who needed 2:19 to beat Maria Kirilenko 6-4, 4-6, 6-2. "It's tough. The courts are real sticky."

She slightly twisted her ankle but said she should be fine by Sunday, when she faces 2004 U.S. Open champion Svetlana Kuznetsova, seeded 14th and one of four Russians to advance Friday.

On the men's side, eighth-seeded Gaston Gaudio of Argentina fell to unseeded Fabrice Santoro of France, appearing in his 55th Grand Slam event.

Masters Cup champion David Nalbandian advanced over No. 26 Jarkko Nieminin. The fourth-seeded Nalbandian, who had a behind-the-back volley winner, will face the winner of the late match between No. 20 James Blake and No. 16 Tommy Robredo.

No. 11 David Ferrer beat No. 18 Mario Ancic 6-3, 6-3, 6-3.

Also advancing were No. 10 Thomas Johansson, the 2002 champion, and No. 11 David Ferrer.

Sharapova routed Jelena Kostanic 6-0, 6-1. The 2004 Wimbledon champion, Sharapova lost to Williams in the semifinals here last year after squandering three match points.

Sharapova, who lost to the eventual champion in all four majors in 2005, said she was no longer seriously bothered by a shoulder problem that sidelined her for two months coming into Melbourne.

Other Russians advancing were No. 6 Nadia Petrova, Kuznetsova and Elena Vesnina.

French Open champion Justine Henin-Hardenne had a 6-4, 6-1 win over Virginie Razzano.