Del Potro joined the fans in standing to applaud. He moved on to a quarterfinal against defending champion Novak Djokovic, who advanced when his opponent, No. 18 Stanislas Wawrinka, stopped because of illness and fatigue while trailing 6-4, 6-1, 3-1.
Djokovic's Serbian Davis Cup teammate, No. 8 Janko Tipsarevic, finished his rain-interrupted 6-3, 7-6 (5), 6-2 victory over No. 19 Philipp Kohlschreiber of Germany, and gets No. 4 David Ferrer of Spain in the quarterfinals.
Olympic champion Andy Murray became the first man to reach the semifinals, coming all the way back after being one point from facing a two-set deficit to beat No. 12 Marin Cilic 3-6, 7-6 (4), 6-2, 6-0.
Four-time major champion Maria Sharapova also turned things around to win her quarterfinal Wednesday, coming from behind after a rain delay for the second consecutive match and defeating 2007 Wimbledon runner-up Marion Bartoli 3-6, 6-3, 6-4.
Sharapova was down 4-0 on Tuesday when play was stopped. But she wound up improving to 12-0 in three-set matches this year.
"It's a great statistic. It shows that I enjoy the battle no matter what the score is," said Sharapova, who will face top-seeded Victoria Azarenka in the semifinals. "The third set, it's the last set out there, and there's no reason why you shouldn't put everything out there."
Serena Williams faced no such trouble in her quarterfinal Wednesday night.
Williams, who has won three of her 14 Grand Slam titles at the U.S. Open, hit 12 aces while defeating 2008 French Open champion Ana Ivanovic 6-1, 6-3.
Williams' semifinal opponent will be 10th-seeded Sara Errani of Italy, who eliminated her good friend and doubles partner, No. 20 Roberta Vinci, in straight sets.
The story of the day, though, was Roddick's departure — from the tournament and from tennis — and Williams watched his loss to del Potro.
"I love Andy so much," Williams said. "Such a good friend."
U.S. Open glance
ON COURT THURSDAY: Men's quarterfinals: No. 2 Novak Djokovic vs. No. 7 Juan Martin del Potro, No. 4 David Ferrer vs. No. 8 Janko Tipsarevic.
ON TV: Tennis Channel, 9 a.m.-5 p.m.; ESPN2, 10 a.m.-9 p.m.
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