Nadal won the last night match before 10:30 p.m. at Rod Laver Arena when Paul-Henri Mathieu retired at 6-4, 3-0 with a left calf muscle injury after losing 11 of the first 12 points of the second set.

Mathieu had taken a medical time-out to receive treatment after the first set, and told the chair umpire after 50 minutes that he could no longer continue.

Nadal said he felt sorry for Mathieu — and himself — that the match finished so quickly.

"I was playing well today, maybe I was playing my best tennis in Australia this year," the three-time French Open champion said. "I'm happy to be in the quarterfinals — would have preferred not like this — but in the quarterfinals anyway."

The last match the previous night did not start until 11:47 p.m. and Lleyton Hewitt finally beat 2006 runner-up Marcos Baghdatis in five sets at 4:33 a.m on Sunday.

The top women raced through the fourth round earlier Sunday, with top-ranked Justine Henin and 2006 finalist Maria Sharapova setting up a quarterfinal showdown.

Henin beat Hsieh Su-wei, the first Taiwanese player through to the fourth round of a Grand Slam event, 6-2, 6-2 in 74 minutes to extend her winning streak to 32 matches.

Sharapova routed No. 11 Elena Dementieva 6-2, 6-0 in 62 minutes.

"I always know to beat her I have to be at my best," Henin said of Sharapova. "She's a real fighter."

The fifth-ranked Sharapova was expected to have a tough time against Dementieva, but broke her fellow Russian's serve six of seven times, including at love to finish off.

"I have always had really tough games against her and I wanted to make sure I kept my focus all the way through," Sharapova said.

Defending champion Serena Williams, who went through periods of inconsistency in her first three matches, was sharper and more consistent in a 6-4, 6-4 win over No. 12 Nicole Vaidisova.

Williams faltered only while serving up a break at 4-3, with Vaidisova breaking to even the set. But Williams broke right back. Vaidosova smashed her racket in anger, then netted a forehand on match point as Williams held at love to finish off the match.

To go along with nine aces, Williams had 23 winners and only 11 unforced errors as she seems to be improving in every match. She next plays No. 3 Jelena Jankovic, a 7-6 (3), 6-1 winner over Australia's Casey Dellacqua.

"Oh, wow. It will be tough for sure," Jankovic said. "We've had some tough matches. I've beaten here a few times, so we will see."

The women's fast work followed the drama Saturday that started with a rare five-setter for Roger Federer and carried on until Hewitt finished off Baghdatis not long before dawn Sunday.

Federer needed 4 hours, 27 minutes to beat 49th-ranked Janko Tipsarevic 6-7 (5), 7-6 (1), 5-7, 6-1, 10-8 in an extended afternoon match that pushed back the night session at least two hours.

Federer had won 30 straight sets at Melbourne Park since dropping the first in the 2006 final against Baghdatis. The Swiss star had lost only six games in his first two matches this year.

"I'm happy I could deliver a five-set thriller. It was good to be part of something like this," said Federer, chasing his third consecutive Australian title and 13th major.

David Nalbandian and Juan Carlos Ferrero stepped back on the same court to begin the Sunday schedule little more than six hours after Hewitt and Baghdatis walked off.

Former No. 1 Ferrero beat 10th-seeded Nalbandian 6-1, 6-2, 6-3 in a third-round match postponed by rain Saturday. In another third-rounder, No. 5 David Ferrer beat American Vincent Spadea 6-3, 6-3, 6-2. Ferrero will play Ferrer in the fourth round.

No. 24 Jarkko Nieminen beat Philipp Kohlschreiber 3-6, 7-6 (7), 7-6 (9), 6-3 and Jo-Wilfried Tsonga edged No. 8 held off fellow Frenchman Richard Gasquet 6-2, 6-7 (5), 7-6 (6), 6-3.