MELBOURNE, Australia (AP) _ Serena Williams is looking over her shoulder as she closes in on the ``Serena Slam.''

The top-ranked Williams won her 24th consecutive Grand Slam match Saturday, overpowering Thailand's Tamarine Tanasugarn 6-1, 6-1 to advance to the fourth round of the Australian Open.

``My priorities still remain to try and stay No. 1,'' said Williams, who has beaten sister Venus in the last Grand Slam finals. ``It's going to be hard because there are lots of people after me _ namely Venus, who really wants to be No. 1 again.''

Serena also has an eye on fourth-seeded Kim Clijsters of Belgium, a possible semifinal opponent.

The 19-year-old Clijsters, a 6-2, 6-1 winner over Belarus' Tatiana Poutchek, has lost only six games in six sets and is averaging just 50 minutes in her three matches. She has won 22 of her latest 23 matches, including consecutive wins over the Williams sisters in the WTA Championships in November.

Men's No. 1 Lleyton Hewitt started slowly, dropping the the first two games to Radek Stepanek, but dominated the rest of the way for a 6-3, 6-2, 6-0 victory. Stepanek, ranked No. 61, had four break points before Hewitt dropped serve in an eight-minute opening game.

``I started a bit rusty tonight and was able to get better and better as it went on,'' Hewitt said. ``We're only in the third round, so you don't want to play your best tennis yet.''

Hewitt, who lost in the first round last year while recovering from chickenpox, said it was a big relief to make the second week at Melbourne Park.

Hewitt's next opponent is Moroccan Younes El Aynaoui, seeded 18th and a U.S. Open quarterfinalist last year, who beat Spaniard Feliciano Lopez 5-7, 6-2, 7-6 (3), 7-6 (8).

Marat Safin, the men's runner-up last year, withdrew from his third-round match against Germany's Rainer Schuettler because of a wrist injury. The third-seeded Safin, who came into the week with a shoulder problem, said his left wrist was too swollen to play.

``I couldn't hold the racket,'' Safin said.

Schuettler will play James Blake, the 23rd-seeded American who advanced beyond the third round for the first time in a major with a 6-3, 4-6, 6-2, 6-2 win over Spain's Alberto Martin.

In other matches, ninth-seeded Roger Federer of Switzerland beat Sweden's Andreas Vinciguerra 6-3, 6-4, 6-2, 25th-seeded Mikhail Youzhny of Russia upset seventh-seeded Jiri Novak of the Czech Republic 6-1, 3-6, 6-3, 6-2, and ninth-seeded American Andy Roddick beat Spain's Fernando Vicente 6-2, 6-3, 6-2.

The 20-year-old Roddick will face Youzhny in the fourth round.

``He won the Davis Cup for Russia, so nothing is going to faze him at the moment,'' said Roddick, who has lost twice to Youzhny. ``I think I'm playing better tennis than the times I've played him before.''

Federer will face Wimbledon finalist David Nalbandian, the 10th-seeded Argentine who led No. 20 Xavier Malisse 4-6, 6-2, 6-0, 3-0 when the Belgian player retired because of fatigue.

``I think Roger is a great player, but I know him from juniors. From a long time ago I beat him two times,'' Nalbandian. ``I think it's going to be a tough match, but I have a strong chance.''

Serena beat Venus in the French Open, Wimbledon and U.S. Open finals last year after missing the Australian Open because of an ankle injury.

``She's never sat down and told me, 'Serena I'm going to take No. 1 away from you.' But I'm sure that's what she wants to do,'' Serena said.

``She's working hard, she's playing really well. She is just on a different level from a lot of the girls and everyone else. When I'm practicing with her, I don't know how I was ever able to beat her. I'm just trying to do what I can to stay in the position.''

Serena's first priority is overcoming No. 18 Eleni Daniilidou of Greece, a 6-4, 6-3 winner over No. 16 Nathalie Dechy of France.

Clijsters will face No. 19 Amanda Coetzer of South Africa, a 6-0, 6-2 winner over No. 14 Anna Pistolesi of Israel.

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. The American will meet No. 8 Anastasia Myskina of Russia, a 6-3, 3-6, 6-3 winner over No. 28 Clarisa Fernandez of Argentina.