Nadal into 4th round; Roddick retires with bum hamstring

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.

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," Roddick said. "You can try to ham and egg it against a lot of guys. But he's really intelligent. He knew what was going on."

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.