By Fitzgerald Cecilio

Top seed Roger Federer advanced to the quarterfinal round of the US Open without hitting a ball after American opponent Mardy Fish withdrew prior to their match due to health concerns.

"I regret that I have to withdraw from the US Open for precautionary measures," Fish said in a statement. "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 reason behind Fish's withdrawal was not immediately known but he earlier missed two months this year due to an accelerated heartbeat and underwent a medical procedure in May.

The American advanced to the last 16 after beating Gilles Simon in a match that went five sets and more than three hours, ending about 1 a.m. Sunday.

Advancing via walkover to the quarterfinal, Federer will face world No. 7 Tomas Berdych, who reached the last eight of the US Open for the first time after beating Spain's Nicolas Almagro, 7-6(4), 6-4, 6-1.

"I am really sorry for Mardy. I just want to wish him a speedy recovery. We all want to see him back on tour soon," Federer said. "It will be a tough match against Tomas. 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."

With the win, Berdych became only the third Czech man to reach the quarterfinals of all four majors, joining Ivan Lendl and Petr Korda.

Both players were sharp early, the opening set coming down to a tiebreak that Berdych seized with four of his 10 first-set aces.

In the second set, Berdych broke Almagro after the latter's sweeping one-handed backhands sailed long, taking a 4-3 edge. After Almagro held serve, Berdych took the next two games to finish the set.

A clearly deflated Almagro, who finished with 31 unforced errors, struggled early in the third set, broken on his first two service games to fall behind 3-0 and never recovered.

Berdych closed out the two-hour contest when an Almagro backhand stab floated wide. He finished with 17 aces and 39 winners.

Meanwhile, 12th seed Marin Cilic of Croatia defeated Martin Klizan of Slovakia, 7-5, 6-4, 6-0 to advance against the winner of the Andy Murray-Milos Raonic match.

In the women's division, No. 12 seed Ana Ivanovic of Serbia defeated Tsvetana Pironkova of Bulgaria, 6-0, 6-4, to reach her first US Open quarterfinal.

"I think I hardly made any mistakes in the first set," said Ivanovic. "She's a tough opponent though and I knew she was going to come back and fight hard, so the second set was tough to come through."

Ivanovic dominated the first set with 13 winners in just six games while converting all three of her break point opportunities to finish it in just 23 minutes.

"It's great to be through to the quarterfinals," said Ivanovic. "It's been a lot of ups-and-downs and having to take time off with injuries since 2008, but finally I've been healthy and it's showing in my tennis."

Ivanovic will play No. 4 seed Serena Williams, who defeated world No. 82 Andrea Hlavackova, 6-0, 6-0 after hitting 31 winners compared to her opponent's nine.

A 14-time Grand Slam champion, Williams committed just seven unforced errors and hit eight aces to finish the match in 57 minutes. She has dropped just 12 games in four matches at the Open this year.

"Andrea played really well," said Williams, who handed out a double bagel for the fifth time in her career. "She never gave up. She's such a great fighter. But I played really well today, I tried to stay relaxed and do what I do. I knew she would be a dangerous opponent."

Meanwhile, 10th seed Sara Errani of Italy ousted sixth seed Angelique Kerber of Germany, 7-6 (3), 6-3, in the last 16 to advance against the winner of the Roberta Vinci-Agnieszka Radwanska match.

Errani will collide with Roberta Vinci of Italy, who ousted No. 2 seed Agnieszka Radwanska, 6-1, 6-4.


US Open: Federer-Berdych Seal Quarterfinal Showdown as Fish Withdraws