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"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."