Hingis, the top seed, battles No. 12 Sandrine Testud of France as she vies for her fourth straight title in Melbourne.

Hewitt, who won two warmup events in his homeland to start the season, will put his 13-0 season record on the line against 12th seed Magnus Norman of Sweden.

Defending men's champion Yevgeny Kafelnikov of Russia, who has put together back-to-back solid performances after a sluggish first-round win, takes on Belgian qualifier Christophe Rochus for the first time. Rochus, 21, is competing in his first Australian Open.

Also, fourth seed Nicolas Kiefer of Germany could have a tough time with former top-10 player Wayne Ferreira of South Africa, and Frenchman Arnaud Clement encounters Younes El Aynaoui in an unseeded matchup. El Aynaoui is one of two Moroccans left in the men's draw, after Hicham Arazi secured a quarterfinal berth on Sunday.

For the women, third seed and reigning U.S. Open champion Serena Williams of the United States could move one step closer to a possible semifinal clash with Hingis if she gets past No. 16 Elena Likhovtseva of Russia.

Williams will attempt to become the third American to reach the women's quarterfinals, joining Lindsay Davenport and Jennifer Capriati, who advanced Sunday.

Sixth seed Barbara Schett of Austria goes against No. 13 Arantxa Sanchez-Vicario of Spain, who lost to Schett in the second round here last year. In addition, 10th seed Conchita Martinez of Spain, a runner-up two years ago, faces unseeded American Kristina Brandi, who upset eighth seed Amanda Coetzer in the second round.

Hingis needed just 51 minutes to dispatch 116th-ranked Alicia Molik of Australia, 6-2, 6-3, on Saturday and has not dropped a set in the tournament.

Hingis has reached the fourth round in 15 of the past 16 Grand Slam events and has won 24 straight matches in Melbourne. The last woman to win four straight Australian Open titles was Margaret Smith, who captured seven in a row from 1960-66.

Testud, a quarterfinalist here in 1998, gave Hingis a tough battle in their last meeting at the Chase Championships in November, losing two straight tiebreakers. The Frenchwoman saved three match points in her third-round win over Tamarine Tanasugarn of Thailand.

Hewitt remained unbeaten in 2000 with a 6-2, 7-5, 6-3 victory over Adrian Voinea of Romania on Saturday. The 18-year-old won back-to-back titles in Adelaide and Sydney but faces his stiffest test so far in Melbourne. Norman has won six titles since the start of 1999, more than any player on the ATP Tour.

"Norman is obviously playing very well," Hewitt added. "But I'm seeing the ball very early and with the way that I'm playing, I'm confident against anyone."

In his last two matches, Kafelnikov has shown no effects of the back injury that first flared at an exhibition event last week and a strained groin suffered in the first round.

After dominating Daniel Vacek, 6-3, 6-0, 6-1 in the second round, Kafelnikov dumped Stefan Koubek of Austria, 6-3, 6-3, 6-4, to reach the round of 16. The Russian has compiled a 19-3 lifetime record in Melbourne, winning his second Grand Slam title here last year.

Americans Andre Agassi, Pete Sampras and Chris Woodruff joined Arazi into the round of eight on Sunday, while ninth seed Julie Halard-Decugis of France and unseeded Ai Sugiyama of Japan advanced to the quarterfinals on the women's side.