MELBOURNE, Australia - Marat Safin injured his ankle, and somehow improved his game in the process.

Safin picked himself up after twisting his right ankle and overcame hard-serving Mario Ancic of Croatia 6-4, 3-6, 6-3, 6-4 today to advance to the fourth round of the Australian Open.

"It ... took all the pressure a little bit from me in the match because I was a little bit uptight," the fourth-seeded Safin said. "When I twisted my ankle, I just kind of stopped a little bit thinking about the way I was playing. And I played quite a good game afterward."

Injuries did continue to take their toll in the season-opening Grand Slam.

Top-ranked Roger Federer was broken in his first service game before getting back on track, and spent less than two sets on center court when Finland's Jarkko Nieminen called it quits with a torn abdominal muscle.

Lisa Raymond lasted only one game of her doubles match before retiring with a strained back muscle, leaving her doubtful for her third-round match Saturday against French Open champion Anastasia Myskina.

Gaston Gaudio, the French Open champion who was seeded 10th, was able to continue after treatment on both thighs, but Dominik Hrbaty upset him in five sets despite 88 unforced errors.

In women's singles, second-ranked Amelie Mauresmo and U.S. Open winner Svetlana Kuznetsova both had straight-set victories and will face unseeded opponents in the fourth round.

Serena Williams, seeded seventh, ended the run of wild-card entry Sania Mirza, the first Indian woman to make it to the second round of a Grand Slam, with a 6-1, 6-4 victory. Williams finishing Mirza off with a second-serve ace, then skipped off the court. She next meets No. 11 Nadia Petrova.

"Finally, after forever it seems, (I was) able to feel my serve," Williams said. "So I was really happy about that."

Wimbledon winner Maria Sharapova, seeded fourth, had a much easier time under the lights than dealing with the daytime heat in her last match, when she needed packs of ice to cool off her neck and shoulders. She needed only 50 minutes to beat China's Li Na, who committed 27 errors and had only three winners in losing 6-0, 6-2.

Eighth-seeded Andre Agassi, seeking his fifth title here, took his baseline game into the night's last match against serve-and-volleyer Taylor Dent.

Safin looked tight while just missing the lines early against Ancic, but broke the 2004 Wimbledon semifinalist in the fifth game. He finished off the first set with a pair of aces after squandering a 40-0 lead.

Ancic swapped his white shirt for a blue one and promptly ran off the next four games. Safin got one break back, but Ancic then held twice at love to even up the match.

Both players became increasingly irritable as their unforced errors piled up, muttering to themselves or yelling in anguish at missed opportunities. Safin, notorious for smashing rackets early in his career, often hung his head or stared at his racket, and at one point rapped his head with his knuckles, trying to regain focus.

"It's a wake-up call," Safin said. "Sometimes my head goes away and doesn't come back - I have to get it back here."

After hitting a forehand long to give Safin a break for a 3-1 lead in the third set, Ancic - back to wearing white again - bashed a towering fly ball that landed in the seats. Safin netted a backhand on the next point and banged a ball just as high that landed near the umpire's chair.

In between the errors, the two men exchanged heavy topspin drives that often caught the tape during long rallies.

After going up 2-0 in the fourth set, Safin tried to push off to go for a backhand, rolled his right ankle and went down as Ancic held to pull within 2-1. Safin already had the ankle taped, as he has over the last two years, and a trainer reinforced the wrap at the changeover.

Safin took his next service game at love with an ace, joking with a line judge who'd earlier called one of his serves wide. He later said the injury relaxed him.

Mauresmo, who beat Serbian teenager Ana Ivanovic 6-2, 7-5, next faces Evgenia Linetskaya, who was a 6-3, 6-4 winner over American Amy Frazier.

"It's a long way still - three matches down, four to go and some good players still in the field," Mauresmo said of the prospects for her first Grand Slam title. "I'm happy with how things are going. Hopefully I get closer and closer to the No. 1 spot."

Kuznetsova made 48 unforced errors in her 6-3, 7-6 (5) win over Mariana Diaz-Oliva.

Earlier in the week, Belgian authorities said Kuznetsova tested positive for ephedrine in a charity match there last month. Kuznetsova said her doctor gave her medicine for a cold. Ephedrine, commonly in cold medicine, is on the list of banned substances in competition, but isn't off limits in the offseason.

In other matches, 15th-seeded Silvia Farina Elia cruised past British qualifier Elena Baltacha 6-1, 6-0.

In other women's matches, 15th-seeded Silvia Farina Elia cruised past British qualifier Elena Baltacha, and 48-year-old Martina Navratilova advanced to the third round of the women's doubles with Daniela Hantuchova.

On the men's side, Thomas Johansson of Sweden, seeded 30th, survived his third consecutive five-set match by downing American Kevin Kim.