NEW YORK - Five-time champion Roger Federer received a walkover into the quarterfinals at the U.S. Open when his scheduled Monday opponent, 23rd-seeded Mardy Fish, pulled out of the draw in New York.

Fish cited health concerns for his withdrawal.

"I regret that I have to withdraw from the U.S. Open for precautionary measures," Fish said. "I was reluctant to do so, but am following medical advisement. I had a good summer and look forward to resuming my tournament schedule in the fall."

The 30-year-old Fish missed nearly three months of action earlier this season due to fatigue issues that led him to a medical procedure to correct a heart problem. He needed a cardiac catheter ablation to deal with misfiring electrical pulses in his heart.

Fish's third-round victory against Frenchman Gilles Simon went five sets, lasting more than three hours before ending after 1 a.m. local time Sunday.

The 31-year-old world No. 1 Federer titled here five straight years from 2004-08 and was the U.S. Open runner-up in 2009. He will meet 2010 Wimbledon runner-up Tomas Berdych on Wednesday.

The amazing Federer, who captured his seventh Wimbledon title in July, will appear in a men's-record 34th straight Grand Slam quarterfinal.

A sixth-seeded Berdych finally reached his first U.S. Open quarterfinal in his 10th trip to Flushing by whipping 11th-seeded Spaniard Nicolas Almagro 7-6 (7-4), 6-4, 6-1 at Armstrong Stadium at the USTA Billie Jean King National Tennis Center. Berdych smacked 17 aces in the two-hour affair.

"At least good that I didn't stay that long on court, that I was able to save some energy, as well," Berdych said.

The 26-year-old Berdych is the third Czech-born male in the Open Era to reach the quarterfinals at all four Grand Slam events, joining Hall-of-Famer Ivan Lendl and Petr Korda.

Berdych is 3-3 in his last six matches against Federer, including a big upset of the Swiss great in the Wimbledon quarterfinals two years ago.

"It will be a tough match against Tomas," Federer said. "We have played many times in the past and he has always been a tough opponent. I will have to continue to serve well and dictate the points."

The last men's day session match on Monday saw 12th-seeded Croat Marin Cilic reach his third career and second U.S. Open quarterfinal with a 7-5, 6-4, 6-0 handling of upstart Slovak Martin Klizan in just over two hours.

Cilic will meet third-seeded Andy Murray, who downed 15th seed Milos Raonic of Canada, 6-4, 6-4, 6-2. Raonic had six double faults, while Murray converted 4- of-12 break points.

The British Murray captured an Olympic gold medal last month and was the 2008 U.S. Open runner-up to Federer.