ESPN Tennis

NEW YORK -- No. 1 Roger Federer won his 38th straight match at the U.S. Open, moving into the quarterfinals with a victory over No. 14 Tommy Robredo.

Federer, in search of his sixth straight title at Flushing Meadows, split the first 10 games against his Spanish opponent Monday before winning 14 of the next 18 for a 7-5, 6-2, 6-2 victory. He was off the court in 1 hour, 48 minutes.

John Isner is out of the U.S. Open, guaranteeing this will be the first time the tournament will not include an American man in the quarterfinals.

"I knew that," Isner said. "I wanted to keep it going."

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Emmanuel Dunand/Getty ImagesNovak Djokovic reached the U.S. Open quarterfinals for the third straight year.

The 55th-ranked American lost 4-6, 6-4, 6-4, 6-4 to No. 10 Fernando Verdasco in the fourth round.

Verdasco, from Spain, will play fourth-seeded Novak Djokovic of Serbia in the quarterfinals, after Djokovic's 6-1, 6-3, 6-3 rout over 15th-seeded Radek Stepanek late Monday.

"First of all I would like to thank all the crowd for staying late," Djokovic told the fans after the match. "New York is a big place and there have been many big matches here at night. It's a privilege for me to play at night. I hope I have more chances to do it."

Isner, who knocked out No. 5 Andy Roddick in the third round with an aggressive serve-and-volley game, hardly used that strategy against Verdasco, an efficient counterpuncher. The 6-foot-9 American came to net on only 27 of 103 points and won barely more than half.

"Maybe I could have done it a little bit better today," Isner said when asked about his net game. "But he, for the most part, just had me on the run. I didn't really stand a chance."

Federer's next match will come against No. 12 Robin Soderling, who he beat in straight sets earlier this year in the French Open final to complete his career Grand Slam.

Soderling has advanced to the quarterfinals of the U.S. Open for the first time after his opponent, Nikolay Davydenko, retired with a leg injury.

Soderling was ahead 7-5, 3-6, 6-2 when the eighth-seeded Russian called off the match. Trainers had been working on Davydenko's left hamstring during a break early in the third set.

Soderling said he had no idea Davydenko was in so much pain.

"I thought that he was moving pretty well. He's a very fast guy, so I was a little bit shocked that he retired," he said.

After retiring from the match, Davydenko refused to get drawn into a conversation about the much-publicized 2008 gambling probe involving one of his matches.

Davydenko was cleared of any wrongdoing after there were suspicious betting patterns in a match he played against a low-ranked opponent in 2007.

"For me, I really don't care now," Davydenko said. "I do it my way, and if I have an injury, I don't want to finish my match."

Before this year's French Open, Soderling had never advanced beyond the third round of a major. At Roland Garros, he upset four-time defending champion Rafael Nadal in the fourth round. Soderling also reached the fourth round at Wimbledon.

Djokovic, runner-up at Flushing Meadows in 2007, was never tested as he raced to victory in 1 hour, 46 minutes.

Stepanek was woeful in the first set and Djokovic took it in just 23 minutes before easing through the second. The Czech put up more of a fight in the third set but a brilliant lob gave Djokovic the break in the sixth game and he marched into the quarterfinals for the third straight year.

Djokovic added to his repertoire of memorable impersonations, channeling his inner John McEnroe in front of a roaring crowd after beating Stepanek.

Djokovic's YouTube-worthy impressions of Maria Sharapova, Nadal and others -- which earned him the nickname "Court Jester" -- haven't always been so well-received.

But the rowdy crowd at Arthur Ashe Stadium was delighted when he turned on the way-back machine after dispatching Stepanek in Monday's final match.

"If the moment is right, it comes spontaneously," Djokovic said. "I thought the moment was right. The crowd loved it, and that was the most important thing."

His McEnroe impression included temper tantrums, swinging volleys and a great, albeit right-handed, send-up of Johnny Mac's lanky, unfurling serve -- a show that will be remembered as much as the material he offered at the '07 Open.

"It was wide!" Djokovic said, pointing to the line, yelling at an empty umpire's chair, as about 10,000 fans in Arthur Ashe Stadium roared.

And, of course, "You cannot be serious!"

McEnroe couldn't resist the bait. Urged by Djokovic to come down and hit a few balls with him -- Todd Martin had already refused -- McEnroe took off his tie and ran down from the TV booth to show Djokovic that nobody can do a better McEnroe than McEnroe.

They played a few points, and after McEnroe strung together a nice serve and one of his perfect, patented, belt-high volleys for a winner, the show was over.

"It actually was quite funny and the crowd loved it. And Johnny, of course, made a small favor coming down," Djokovic said. "It wasn't easy playing in jeans and suit and collared shirt but it was a lot of fun.

"I like to entertain the crowd," he added. "That makes me happy as well. Playing with Johnny Mac and having fun, I think that's what the crowd want, and especially in this hour, these night matches make this tournament very special."

Information from The Associated Press and Reuters was used in this report.