Andre Agassi survived his biggest test of the US Open thus far but got some help from Taylor Dent's injured right leg.
Top-seeded Agassi dropped the first set before rallying for a 6-7 (5/7) 6-4 7-5 victory over Dent, who was forced to retire after the third set due to tightness in his lower right hamstring.
Agassi cruised in the first three rounds of the tournament, despite enduring a third-round match with Russia's Yevgeny Kafelnikov that took two days to complete due to rain.
Rain again was a factor, pushing Agassi's match with his fellow American, which was originally scheduled for Monday, back to a 11pm Irish time start.
It was the first match of the day at the USTA Tennis Centre after the wet weather forced numerous matches to be postponed.
Agassi dropped his first set of the tournament when Dent used his powerful serve to win the first-set tiebreaker. Dent started limping after serving early in the second set and had a 2-1 lead when he asked to see the trainer, a request that was denied until the players changed sides.
The trainer massaged Dent's right leg twice in the second set as Agassi rallied, breaking the serve of his 22-year-old countryman to win the set.
Dent also was up 2-1 in the third set before finally getting the injury taped heavily, but he seemed to have little mobility and strength in the leg thereafter.
Agassi narrowly won the third set, taking advantage of his opponent's 14 unforced errors, and advanced to the quarter-finals when Dent finally gave in to the injury.
Had the match continued, it would likely have been suspended a fourth time as rain came shortly after, suspending the six matches that had commenced or been resumed.
Third seed Juan Carlos Ferrero of Spain, the reigning French Open champion, has a 6-2 lead over American veteran Todd Martin in a match that was originally scheduled for Monday.
In other matches suspended, fifth seed Guillermo Coria of Argentina has a comfortable 6-2 2-0 lead on Sweden's Jonas Bjorkman, and 11th seed Paradorn Srichaphan, the Thai who won a tune-up event on Long Island just before the US Open, has a 4-3 edge over sixth seed Lleyton Hewitt of Australia.
Fourth seed Andy Roddick was scheduled to play the featured night match against Belgian Xavier Malisse, but the contest never began.
On the women's side, seventh seed Anastasia Myskina of Russia leads Mary Pierce of France 7-6 (7/2) 2-0 with the winner to take on second seed Justine Henin-Hardenne of Belgium in the quarter-finals.
The 15th seed, Ai Sugiyama of Japan, was on the verge of defeating 29th seed Francesca Schiavone of Italy 7-6 (7/5) 5-4 before the players were taken off the court. The winner meets sixth seed Jennifer Capriati for a spot in the semi-finals.
Earlier, five matches on both sides of the draw were postponed until a later date. Wimbledon champion Roger Federer of Switzerland had his match with 13th seed David Nalbandian of Argentina suspended, as did seventh seed Carlos Moya of Spain, who will face 22nd seed Younes El Aynaoui of Morocco.
Eighth seed Rainer Schuettler of Germany was forced to wait for his contest against 12th seed Sjeng Schalken of the Netherlands.
On the women's side, top seed Kim Clijsters of Belgium will not face fifth seed Amelie Mauresmo of France until today at the earliest while American Lindsay Davenport, the third seed, had her match with 24th seed Paola Suarez of Argentina delayed.
Rain is forecast into this afternoon and clear skies are not expected until Saturday. Further delays could cause significant scheduling problems.