World number one and top seed Roger Federer was sent into the fourth round of the Australian Open after his opponent Jarkko Nieminen retired with an abdominal injury during their match in Melbourne on Friday.

Swiss Federer was leading 6-3, 5-2 at the time when the Finn called a halt after dropping serve for the third time in the second set.

Federer faces either 13th-seeded Spanish Tommy Robredo or Marcos Baghdatis of Cyprus in the round of 16 on Sunday.

Fourth seed Marat Safin, former US Open champion and two times finalist at Melbourne Park, overcame a second set loss and defeated Croat Mario Ancic 6-4, 3-6, 6-3, 6-4 to win.

But French Open champion Gaston Gaudio, 10th seed at Australian Open, was outclassed by Slovakian Dominik Hrbaty 7-6, 6-7, 6-7, 6-1, 6-3.

However, the loss equaled Gaudio's best performance at the Australian Open, a third round appearance in 2003.

Women's second seed Amelie Mauresmo from France beat 17-year-old Ana Ivanovic from Serbia and Montenegro 6-2, 7-5. In the first set, Mauresmo had a perfect score of points won at the net --100 percent.

Although the percentage dipped only a little to 92 percent in the second set, she faced unexpected stronger resistance from her opponent before managing a final win.

"I should go into the net more often, the percentage was great," said Mauresmo after the match.

"The second set was a little more tight but in the key moments I think I made the difference," she said.