Andre Agassi put in an impressive display as he edged out Croat Ivo Karlovic 7-6 (7-4) 7-6 (7-5) 7-6 (7-4).
Karlovic, 6ft 10ins, hammered down 30 aces and saved 10 of 11 break points against him but Agassi's experience shone through in the tie-breaks.
The seventh-seeded American faltered only once when he allowed a 4-1 advantage to slip in the second set.
Agassi is likely to face another stern test in the next round when he takes on Tomas Berdych of the Czech Republic.
Berdych, who beat Roger Federer at the Olympics last year, overwhelmed Brazilian Ricardo Mello 6-3 6-2 6-0.
But Agassi is also in good form and has now drawn level with Ivan Lendl on 73 wins at the US Open, with only Jimmy Connors ahead on 98.
The Las Vegan said it had been a unique challenge to play Ivo Karlovic - a player nearly a foot taller than him.
"There are moments out there that are really awkward," he said.
"You just don't expect somebody to be able to cover that much ground by just sticking out their racquet.
"You have to concentrate point after point. You never know when the match is decided against a player like that."