NEW YORK – Andy Roddick reached the U.S. Open quarterfinals thanks to another abbreviated work day.

Mr. Roddick, the 2003 champion and 2006 runner-up, advanced today when his fourth-round opponent, No. 9-seeded Tomas Berdych, stopped playing in the second set because of what appeared to be a breathing problem.

“I’ll probably head out to the practice courts right now,” said the fifth-seeded Mr. Roddick, who could face No. 1 Roger Federer next.

Mr. Roddick was leading 7-6 (6), 2-0 when Mr. Berdych quit, making him 0-9 against top-10 opponents at Grand Slam tournaments. Mr. Roddick’s second-round opponent, Jose Acasuso, stopped while trailing two sets to one.

Earlier today, 2004 champion Svetlana Kuznetsova got off her stomach and closed the match, beating Victoria Azarenka 6-2, 6-3 to reach the quarterfinals.

Ms. Kuznetsova needed five match points, finishing it off with a strong, cross-court forehand that Ms. Azarenka chased into the corner, losing her hat on the way.

Earlier in the second set, No. 4 Ms. Kuznetsova was the one who tried without success to track down a shot. In the sixth game, she charged toward the net and skidded, doing the splits and winding up sprawled on the court.

The Russian got up easily and went on to eliminate the 18-year-old from Belarus. Ms. Kuznetsova next plays another unseeded opponent, Agnes Szavay of Hungary.

Ms. Szavay moved on by defeating Julia Vakulenko of Ukraine 6-4, 7-6 (1). Ranked No. 31, Ms. Szavay is playing in her first U.S Open – her two other previous Grand Slam appearances ended in second-round losses at Wimbledon and the French Open this year.

Later in the day, No. 6 James Blake was to face No. 10 Tommy Haas, and Mr. Federer was to meet Feliciano Lopez at night.