Serena Williams was back in "Serena slam" form Thursday.

After nearly losing her opener, Williams advanced to the Australian Open's third round with a 6-4, 6-0 victory over Belgian Els Callens, who gave the world's No. 1 player a tough challenge at Wimbledon last year. Williams now is five matches away from becoming the reigning champion of all four major tournaments.

Her potential semifinal opponent, No. 4 Kim Clijsters, advanced with a 6-0, 6-0 victory over Hungary's Petra Mandula in 33 minutes. It was the first perfect score line of the tournament.

Meanwhile, Czech player Radek Stepanek, who climbed from 547th to 63rd in the rankings last year, knocked out three-time French Open champion Gustavo Kuerten, who never has advanced beyond the second round in the Australian Open. Stepanek won 5-7, 6-3, 7-5, 4-6, 6-3 in 3 hours 47 minutes.

Kuerten, seeded 30th, became the 13th casualty among the 32 seeded men. The top 10, however, is missing only No. 5 Carlos Moya, a 3-6, 7-6 (10-8), 6-4, 4-6, 6-2 loser to American Mardy Fish on Wednesday night.

Third-seeded Marat Safin, the 2000 U.S. Open champion and last year's Australian runner-up, advanced by beating France's Albert Montanes, 6-3, 4-6, 6-4, 6-1. No. 6 Roger Federer defeated Germany's Lars Burgsmuller, 6-3, 6-0, 6-3.

Last year, an injury on the eve of the Australian Open ruined Serena's chance for a true Grand Slam -- winning all four majors in the same calendar year. She went on to beat sister Venus in the finals at the French Open, Wimbledon and U.S. Open.

A rash of errors left Serena on the verge of defeat before she rallied to edge France's Emilie Loit on Tuesday. This time, she said she was inspired by Venus's 6-3, 6-0 victory over Ansley Cargill the previous night.

"She played a great match," Serena said of Venus. "I was motivated after watching her, thinking, 'Okay, she wants to be No. 1 again.' "

In the opener here, Serena acknowledged being "a little too lackadaisical" against Loit. She vented her frustration in that match with an audible obscenity, for which she was fined $1,500 on Thursday.

She had few troubles this time. She hit 21 winners to Callens's eight and had 19 errors to Callens's 20.

"I have five more matches to go. It's going to be really tough," Serena said, noting that Clijsters and No. 6 Monica Seles are in her half of the draw.

Seles beat Venus in the quarterfinals here last year. Clijsters beat both sisters on her way to winning the WTA Tour Championships in November.

As for playing against her sister, Serena said, "We've gotten use to it. If it comes to the final, at least we've both reached our maximum potential."

Serena next plays No. 26 Tamarine Tanasugarn, a 6-2, 3-6, 6-3 winner over Russian Alina Jidkova.

Lindsay Davenport, who has won three majors including the 2000 Australian, had to rally from a 3-1 deficit in the final set for a 6-7 (9-7), 6-4, 7-5 victory over 57th-ranked Iroda Tulyaganova of Uzbekistan. Davenport was helped by a series of errors by her opponent in the final game.