MELBOURNE, Australia (AP) - Rafael Nadal moved into the fourth round of the Australian Open without dropping a set or showing any signs that a freak knee injury is bothering him.
Second-ranked Nadal had a 6-2, 6-4, 6-2 win Friday over Slovakia's Lukas Lacko, the last qualifier in the draw, and will next play either John Isner or Feliciano Lopez.
Nadal, who won the 2009 Australian title but has gone out in the quarterfinals due to injuries in the last two years, felt a crack and then sharp pain in his right knee while sitting in a chair at his hotel on the weekend and was concerned that he might not be able to play in his opening match. Medical tests didn't show any serious damage, and he has had the knee heavily taped in his three matches since.
"The knee is fine. That's important thing," the 10-time major winner said. "The match was a really complete match, a really solid one.
"Very happy about my game. Being in fourth round without losing a set, it's fantastic news."
Nadal is on the same half of the draw as Roger Federer at a major for the first time since 2005. Federer, who has won four of his 16 Grand Slam titles in Australia, was playing Ivo Karlovic in the following match on Rod Laver Arena.
On the women's side, top-seeded Caroline Wozniacki continued her quest for a first major title with a 6-2, 6-2 win over Monica Niculescu of Romania and third-seeded Victoria Azarenka beat beat Mona Barthel 6-2, 6-4 in a match between champions of two warmup tournaments.
No. 8 Agnieszka Radwanska beat Kazakhstan's Galina Voskoboeva 6-2, 6-2 and will next meet No. 22 Julia Gorges, who beat Italian Romina Oprandi 3-6, 6-3, 6-1.
Wozniacki, who needs to reach the quarterfinals to have any chance of retaining the No. 1 ranking, wasted one match point and was broken when she was serving for the match, but broke back immediately to ensure she moved into the Round of 16.
Azarenka, who beat French Open champion Li Na to win the Sydney International last week, has only lost eight games at Melbourne Park and remains one of three women who can overhaul Wozniacki for the top ranking at the Australian Open.
The 22-year-old from Belarus will next meet Czech player Iveta Benesova, who beat Russian qualifier Nina Bratchikova 6-1, 6-3.
Barthel was on a 10-match winning run in Australia after capturing her first title at the Hobart International last week as a qualifier.
Barthel hit 20 winners - one more than Azarenka - but she was broken three times and failed to convert three break opportunities.
Azarenka was annoyed with herself for needing five match points to finish off Barthel, and for running out of challenges before she really needed to review a line call in the last game.
"I've been playing in the end not brave enough to finish the match ... I had to get a little," angry, Azarenka said.
Andy Roddick is already out of the tournament, retiring during his second-round match against Australian veteran Lleyton Hewitt late Thursday.
He needed a medical timeout after injuring his right hamstring in the second set and played 16 more games before finally retiring when Hewitt gained a 3-6, 6-3, 6-4 lead.
"It's a miserable, terrible thing being out there compromised like that," Roddick said.
The 29-year-old American knew he wouldn't be able to fool an opponent he was playing for the 14th time, one of the few players on the tour older than he is, somebody who was ranked No. 1 before he was and someone with one more Grand Slam title.
"He's a tough guy to play," said Roddick, now 7-7 against Hewitt for his career. "You can try to ham and egg it against a lot of guys. But he's really intelligent. He knew what was going on."
When he knew he needed to win two more sets to advance, he called the trainer, then walked over to shake Hewitt's hand.
"I was hitting the ball as well as I could from a compromised position and still felt like I was just hanging on," he said. "I don't know that it would have been smart to do that for two more sets. And if somehow you pull a rabbit out of the hat, I don't think you play in two days. If I'm looking at timelines, I think there's three weeks or so before I have to play again."
Hewitt, who turns 31 next month, goes to the third round against Milos Raonic, the big-serving, 21-year-old Canadian. If Hewitt eliminates an opponent who has dropped only two service games this year, he could face defending champion Novak Djokovic in the fourth round. Djokovic, who won three of the four major titles last year, kept getting better in his 6-3, 6-2, 6-1 win over Santiago Giraldo.
Fourth-seeded Andy Murray, who lost to Djokovic in last year's Australian final, ousted Edouard Roger-Vasselin of France 6-1, 6-4, 6-4. No. 5 David Ferrer beat American Ryan Sweeting 6-7 (4), 6-2, 3-6, 6-2, 6-3, and No. 6 Jo-Wilfried Tsonga downed Ricardo Mello of Brazil 7-5, 6-4, 6-4.
Five-time Australian Open champion winner Serena Williams notched her 500th career singles victory Thursday when she beat Barbora Zahlavova Strycova 6-0, 6-4 in the second round.
"Five hundred is a lot of matches to play, let alone to win," she said, adding that the left ankle she badly sprained two weeks ago wasn't an issue. "It's totally fine. It was my good ankle, so I'm good."
Williams won the Australian Open in 2009 and 2010, but didn't defend her title in 2011 because she was injured.
No. 2 Petra Kvitova moved into the third round with a 6-2, 2-6, 6-4 win over Carla Suarez Navarro. Maria Sharapova, one of the three former champions in the women's draw, routed U.S. qualifier Jamie Hampton 6-0, 6-1. No. 7 Vera Zvonareva, a two-time semifinalist at Melbourne Park, No. 9 Marion Bartoli and No. 21 Ana Ivanovic all advanced.
