WIMBLEDON, England -- Top-seeded defending champion Rafael Nadal overcame a foot injury and outlasted Juan Martin del Potro 7-6 (6), 3-6, 7-6 (4), 6-4 in a Centre Court duel that ended in fading light shortly after 9 p.m.
A grimacing Nadal took a medical timeout after hurting his left foot in the game before the first-set tiebreaker. A trainer sprayed and taped the foot. Nadal fell behind 3-0 in the tiebreaker and was limping between points, but saved a set point at 6-5 down and took the tiebreaker on his fourth set point when Del Potro double-faulted.
Nadal says he initially thought he might have broken his left foot in his hard-fought match and he's worried whether he'll be fit for his quarterfinal against Mardy Fish, who beat 2010 runner-up Tomas Berdych 7-6 (5), 6-4, 6-4.
"For a moment at the end of the first set, I thought that I had to retire," Nadal said. "I didn't know what's going on. After that, the pain goes a little bit down and finally I was ready to play."
Nadal said he would get an MRI exam on the foot and couldn't be 100 percent sure how fit he'll be for his quarterfinal Wednesday against the 10th-seeded Fish.
"I'm worried, for sure. I'm going to do the MRI. We'll see what's going on. Tomorrow, we will see," Nadal said. "I cannot predict the future."
After winning the second set, Del Potro needed his own medical timeout after slipping and falling at the baseline at 2-2 in the third. He stayed on the ground for several seconds, grabbing his left hip. After treatment in the locker room, Del Potro came back and didn't seem bothered by the injury.
Nadal broke for the first time to go up 3-2 in the fourth set with a forehand winner down the line. He maintained the advantage and served out the match at love after nearly four hours. Nadal finished with 61 winners to just 16 errors.
Djokovic, who can replace Nadal as the top-ranked man in the world by reaching the final, beat Michael Llodra of France 6-3, 6-3, 6-3.
Federer dropped his first set of the tournament before coming back to down Mikhail Youzhny
6-7 (5), 6-3, 6-3, 6-3 and reach his 29th successive Grand Slam quarterfinal. Extending his career record against the Russian to 11-0, Federer had 54 winners, including 14 aces, and broke five times.
"I forgot completely (the 29th quarterfinal) was on the line to be quite honest, especially once you're in the heat of the moment, of the battle," said Federer, who also won his 100th match on grass. "I thought I played a good match overall."
Murray, who faced the added pressure of playing in front of royal newlyweds Prince William and the former Kate Middleton, moved into the quarterfinals by beating Richard Gasquet of France 7-6 (3), 6-3, 6-2 Monday.
After shaking hands with Gasquet, Murray waved to three sides of Centre Court and then turned and bowed toward the royal couple, who were standing and applauding.
"If I'd known they were coming, I would have shaved," the Scot said with a smile. "I was thinking to myself as I came off I was sweaty and very hairy. I said to them, 'I'm sorry, I'm a bit sweaty.' But it was really nice."
Murray has now reached the Wimbledon quarterfinals four straight years. He made the semifinals the last two years.
Murray's next opponent is unseeded Feliciano Lopez, who came from two sets down and saved two match points in the third set tiebreaker to overcome Polish qualifier Lukasz Kubot 3-6, 6-7 (5), 7-6 (7), 7-5, 7-5. Lopez served 28 aces.
The 29-year-old Fish reached the Wimbledon quarterfinals for the first time by beating Berdych of the Czech Republic. He has never been to the semifinals of a Grand Slam tournament. He was a quarterfinalist at the 2007 Australian Open and 2008 U.S. Open.
Fish, who is seeded 10th, hit 23 aces Monday and saved both break points he faced. He finished with 42 winners and only 12 unforced errors. He won the point on 20 of 25 trips to the net.
The sixth-seeded Berdych hadn't lost a set through his first three matches.
Djokovic will next face Australian teenager Bernard Tomic, a qualifier who defeated Xavier Malisse earlier in the day to become the youngest quarterfinalist at the All England Club since Boris Becker in 1986.
Tomic, who eliminated two-time French Open runner-up Robin Soderling, is one of two qualifiers in the fourth round this year, along with Kubot.
Tomic is 18 years old, 29 days older than Becker when the German reached the quarters in 1986. Becker won the tournament that year, defending his title.
"Unbelievable achievement. I feel great. Great honor to do it here in Wimbledon," said Tomic. "I'm not going to stop now. I'm going to try my best to play on Wednesday in the quarters. I've got nothing to lose."
He'll likely need his best tennis to continue in the tournament, especially against the one player on tour who knows his game the best -- Djokovic.
The pair share a common language in Serbo-Croatian and have hit together several times since playing an exhibition match in Australia at the beginning of last year.
"He's a cool guy. One of the nicest guys out there on the tour," Tomic said of the two-time Australian Open champion. "To play against a guy like him that's (No.) 2 in the world, it doesn't get really better than that."
When they do play, it will be for the second time this year at Wimbledon following a practice set before the tournament.
"He destroyed me," Tomic said, then smiled as he continued. "Things are not looking good for me, but hopefully he destroyed me then and not on this game on Wednesday."
Information from The Associated Press was used in this report.