Russian Marat Safin, the 2000 champion, was up by a break at 2-1 over 14th-seed Tommy Haas of Germany when rain halted play at the US Open today.
In the other fourth-round game, seventh-seeded Nikolay Davydenko of Russia held a 6-1, 5-7, 6-3 lead over 17th-seeded Scot Andy Murray, but it does not appear there will be any more play in either game until tomorrow.
Two-time defending champion Roger Federer was set to take on unseeded Frenchman Marc Gicquel in the night session.
Gicquel will have to hope the delays upset the rhythm of the world's top player, who is yet to drop a set at Flushing Meadows and lost just six games to American Vincent Spadea in he third round.
The 79th-ranked Gicquel had to scramble for a 6-0, 4-6, 4-6, 6-1, 7-6 (7-3) triumph over No 21 Gaston Gaudio on Sunday.
The winner will face either fifth-seeded American James Blake or number 12 Tomas Berdych of the Czech Republic in the quarter-finals.
