Nadal needs fourth set in Melbourne

MELBOURNE, Australia -- Defending champion Rafael Nadal advanced to the fourth round of the Australian Open on Friday along with Andy Murray, U.S. Open champion Juan Martin del Potro, Andy Roddick and Fernando Gonzalez.

Nadal, who beat Roger Federer in last year's final, held off Philipp Kohlschreiber of Germany 6-4, 6-2, 2-6, 7-5 in a night match.

In the fourth round, Nadal will play Ivo Karlovic, who beat Ivan Ljubicic 6-3, 3-6, 6-3, 7-6 (7). The 6-foot-10 Karlovic holds the tour record for the most aces in a match with 78.

"He's a really difficult opponent because the match is decided in a few points," Nadal said. "So the thing is to concentrate with my serve all the time and try to convert the small opportunities that I can have on the return."

The fifth-seeded Murray, bidding to win his first Grand Slam singles title, beat Florent Serra of France 7-5, 6-1, 6-4 and is one victory away from a potential quarterfinal with Nadal.

First, Murray will have to beat American John Isner, who won at Auckland last week for his first ATP title. The 6-foot-9 Isner continued his strong play by defeating 12th-seeded Gael Monfils of France 6-1, 4-6, 7-6 (4), 7-6 (5).

"I was just kind of riding a wave of momentum, and I still am," Isner said. "Hopefully, I can keep it going."

No. 4 Del Potro beat Florian Mayer of Germany 6-3, 0-6, 6-4, 7-5 and No. 7 Roddick advanced 6-7 (4), 6-4, 6-4, 7-6 (3) over Feliciano Lopez of Spain.

Next up for del Potro is Marin Cilic, who stopped Stanislas Wawrinka 4-6, 6-4, 6-3, 6-3.

Gonzalez, the 2007 finalist, beat Evgeny Korolev of Kazakhstan 6-7 (5), 6-3, 1-6, 6-3, 6-4. Roddick and Gonzalez will play each other in the fourth round.

Gonzalez was supported Friday by a throng of noisy, flag-waving Chilean fans on Show Court 2. Roddick is wary of his next opponent, despite holding an 8-3 edge in career meetings and a straight-sets win the last time they met at the 2008 U.S. Open.

"He's a very dangerous player," the 2003 U.S. Open champion said. "Some days he comes out, looks like he's playing Ping Pong the way he can sling the ball around. I don't think there are going to be a lot of secrets out there."