Wimbledon, England ? Top-ranked Rafael Nadal rallied for another five-set victory Saturday, overcoming knee problems, an umpire’s warning and a tough challenge from a hard-hitting German to reach the fourth round of Wimbledon.

Nadal battled back from two-sets-to-one down for the second straight match to defeat Philipp Petzschner, 6-4, 4-6, 6-7 (5), 6-2, 6-3, in a Centre Court slugfest.

Defending women’s champion Serena Williams had a much easier time, serving 19 aces in a straight-sets win over Dominika Cibulkova that set up a fourth-round matchup with former champion Maria Sharapova.

The top-seeded Williams had at least two aces in each of her nine service games and overpowered the 46th-ranked Slovak 6-0, 7-5.

The second-seeded Nadal, who won the title in 2008 but missed last year’s tournament due to tendinitis in his knees, called for the trainer four separate times for treatment on his left arm and right knee.

“I hope I’ll be fine,” Nadal said afterward. “I don’t know. I’m going to check. It’s not a big problem. It’s a long season for me. I have played a lot of matches the last few months.

“Having a five-set match two days ago and one today — that’s tough. I’m happy to be in the fourth round. I’m going to try to be better for Monday.”