Andy Roddick made the US Open quarter-finals when Tomas Berdych retired ill, and he now faces defending champion Roger Federer.
Former US Open champion benefits from another injured opponent.
Andy Roddick was handed a place in the US Open quarter-finals on Monday, when Tomas Berdych was forced to retire through illness, while Roger Federer's bid for a third consecutive title remains on course.
Federer dropped the opening set against Feliciano Lopez in just 25 sparkling minutes of tennis from the Spaniard.
The Swiss world number one hit back with a break handing him the second set, and he then took full charge of the match, taking 32 service points on the bounce at one point.
11 aces and ten services game to love saw Federer win through 3-6 6-4 6-1 6-4 to move into the quarter-finals and a showdown with former champion Andy Roddick.
The American fifth seed had led 7-6 (8-6) 2-0 in his match against Berdych when his ninth-seeded opponent was forced to quit the contest with a stomach problem.
2003 champion Roddick will now have a real test in the last eight date with defending champion Federer now lying in wait and looking in ominous form.
Roddick should be fresh for a rematch of last year's final, having also seeing his second round opponent Jose Acasuso retire, with A-Rod leading 4-6 6-1 6-2 at the time.
Disappointment
Despite not really having been tested so far in the tournament, Roddick insisted it was a disappointment not to have claimed a proper victory.
He explained: "You don't want to advance because someone isn't feeling well."
After consultation with medical staff at Flushing Meadows, Berdych confirmed he had been in some discomfort throughout the match.
"I'm not feeling well," he said after the match. "I have just been in the doctor's.
"I'm going to go back there again to have a blood test.
"I was feeling really bad throughout the match. I was just trying and hoping that maybe it was going to get better. But it didn't."
Elsewhere
Tommy Haas pulled off a shock 4-6 6-4 3-6 6-0 7-6 victory over American sixth seed James Blake meanwhile.
The German will now take on Russia's Nikolay Davydenko in the last eight, after the fourth seed overcame South Korean Hyung-Taik Lee.
Last year's semi-finalist cruised through his match against Andy Murray's conqueror 6-1 6-3 6-4 at the Louis Armstrong Stadium.
He cracked 31 winners and faced just two break points in the match to set-up a rematch of last year's quarter-final between the two.
