Even with an ailing leg, Nadal is tough to beat

Even with an ailing right leg, Rafael Nadal can conjure some of his best tennis.

The defending champion at Wimbledon returned to the court Saturday and managed to get through two sets against Gilles Muller without committing a single unforced error, winning 7-6 (6), 7-6 (5), 6-0 in the third round.

The match started Friday but was suspended because of rain after the first set. Just before the interruption, Nadal had called for a trainer after falling to the turf while winning the tiebreaker. He said it was a muscle problem, but did not elaborate.

Nadal, who has not been defeated at the All England Club since losing to Roger Federer in the 2007 final, said his leg was a "little bit more tired than usual."

"But this is not limiting my game," he said. "I can play with that without problems."

It certainly didn't appear to bother him against Muller, the last man other than Federer to beat Nadal at Wimbledon.

Both players held serve in the second set when the match resumed on Court 1, and Nadal earned a mini-break at 5-5 in the tiebreaker. He then won the next point on his serve and didn't lose another game.

"The third set, two sets to love, I am able to play with less pressure," said Nadal, who lost to Muller in the second round in 2005. "I started to return unbelievable and to play at very high level, I think."

After losing to Federer in the 2006 and '07 finals, Nadal beat the Swiss great in the 2008 championship match. He missed the 2009 tournament because of injury, but won again last year.

In the fourth round, Nadal will face 2009 U.S. Open champion Juan Martin del Potro. The 24th-seeded Argentine - the only other man to beat Federer in a Grand Slam final - defeated Gilles Simon of France 7-6 (8), 7-6 (5), 7-5.

"Of course on Monday I play against the best player in the world in this moment. It will be a big challenge," Del Potro said, adding he will have to play "unbelievable" tennis to win. "You should play everything perfect, and then maybe you have a little chance."

Nadal is 5-2 against Del Potro, including two wins this year.

"When he's healthy, he must be in the top five ... So will be a very tough opponent for me. I know that," Nadal said. "I'm not lucky to play against Del Potro in the round of 16."