-- One embarrassing swing-and-miss aside, Serena Williams is steadily sharpening her game as she draws within four victories of a "Serena Slam."

Williams needed only 46 minutes to beat Thailand's Tamarine Tanasugarn, 6-1, 6-1, Saturday and advance to the fourth round of the Australian Open.

She hit 27 winners, but her eight errors included a complete miss on an overhead smash in the second set's first game.

Kim Clijsters, considered one of the most likely to stop Williams from winning a fourth consecutive Grand Slam tournament, won 6-2, 6-1 in 55 minutes against Tatiana Poutchek. She has lost just six games in six sets.

If she and Serena keep advancing, they would meet in the semifinals.

Meanwhile, Marat Safin, last year's runner-up, withdrew with a wrist injury from a fall in his first-round match.

The 2000 U.S. Open champion's withdrawal sent No. 31 Rainer Schuettler into the fourth round against No. 23 James Blake, a 6-3, 4-6, 6-2, 6-2 winner over Spain's Alberto Martin.

Safin, who had been coming back from a shoulder injury, said an injection helped him through his second-round victory over Spain's Albert Montanes but afterward his left wrist swelled up badly.

Williams won the French and U.S. Opens and Wimbledon last year.

"I've picked up my game. If I'd been at lower level it would have been a lot closer," said Williams, who came close to losing her first-round match against France's Emilie Loit.

She was expecting a hard year "because a lot of people are after me, namely Venus, who wants to be No. 1 again."

Older sister Venus is in the other half of the draw, and could meet Serena in their fourth consecutive Grand Slam final.

Next up for Serena is No. 18 Eleni Daniilidou, a 6-4, 6-3 winner over No. 16 Nathalie Dechy.

Clijsters, who beat both Williams sisters in a tournament last November, improved her record to 22 victories in 23 matches.

She has spent just 21/2 hours on the court in three rounds here, but also showed a perfectionist side, throwing down her racket after a miss when the 108th-ranked Poutchek, from Belarus, held serve in the second set's sixth game.

No. 10 Chanda Rubin reached the fourth round for a fourth consecutive Grand Slam with a 6-3, 6-2 victory over Austrian qualifier Barbara Schwartz.

She next meets No. 8 Anastasia Myskina, who reached her first fourth round at a major by beating No. 28 Clarisa Fernandez of Argentina, 6-3, 3-6, 6-3.

Another Russian, Elena Bovina, beat No. 11 Magdalena Maleeva, 7-5, 4-6, 7-5. She next plays No. 25 Meghann Shaughnessy.

Shaughnessy won 6-1, 6-3 against Czech player Klara Koukalova, who narrowly beat out No. 6 Monica Seles in the second round after Seles sprained her ankle in the third game.

On the men's side, No. 6 Roger Federer ousted the last surviving qualifier, Sweden's Andreas Vinciguerra, 6-3, 6-4, 6-2.

He next plays Wimbledon runner-up David Nalbandian, who advanced when No. 20 Xavier Malisse withdrew because of fatigue. No. 10 Nalbandian was leading 4-6, 6-2, 6-0, 3-0.

Blake, part of the rising American generation, reached the fourth round for the first time at a major by evening his record against Martin at 1-1.

"I had a little jitters at the beginning. Once I got through that, it was great," said Blake, who hit nearly twice as many winners as his opponent.

No. 18 Younes El Aynaoui, a U.S. Open quarterfinalist last year, beat Spain's Feliciano Lopez 5-7, 6-2, 7-6 (7-3), 7-6 (10-8).

On Friday, Andre Agassi needed every shot in his repertoire to beat hard-hitting Nicolas Escude.

Agassi scrambled, volleyed and swatted baseline winners off his shoelaces to win ,6-2, 3-6, 6-3, 6-4, and advance to the fourth round.

Kim Clijsters strikes a forehand during third-round match against Tatiana Poutchek on Saturday. Clijsters needed just 55 minutes for 6-2, 6-1 victory.