Andre Agassi began his 19th US Open campaign with victory over fellow American Robby Ginepri on Monday night.
The former world number one was made to work hard by his compatriot but got breaks at the crucial times for a 7-6 6-4 6-2 victory.
Agassi struggled to find his usual dominant form as inconsistent serving repeatedly gave Ginepri chances.
But, spurred on by the New York crowd, the 35-year-old came through and meets Florian Mayer or Flavio Saretta next.
"I managed to fight hard in a lot of those rallies and won the crucial points," said Agassi.
Mayer and Saretta's match was suspended due to bad light with Mayer leading 6-4 6-2 5-1.
Roger Federer and Carlos Moya made steady starts earlier on Monday.
Top seed Federer was not at his best but still swept past former French Open champion Albert Costa 7-5 6-2 6-4.
Federer made hard work of closing out the match against Costa, dropping serve when trying to wrap up the win in the third set, but was pleased enough with the victory.
"I felt I had some very good moments attacking, some very good moments defending, and it's something I can build on," said Federer.
And the Australian Open and Wimbledon champion admitted that he is eager to match Mats Wilander's 1988 feat of winning three Grand Slams in a year.
"If I could go three out of four that would be an incredible record," he said.
"That would be enough for me. You know I would be the second after Wilander to do it. But we are not there yet. Let's just be patient."
Moya, seeded third at Flushing Meadows, fought back against American Brian Baker to win 6-7 (6-8) 6-4 6-4 6-2.
The Spaniard conceded he had found the early stages of his match against Baker hard going.
"It was very hot and humid out there and I started badly, my legs were a bit weak when we finished the first set ," said the Spaniard.
"My forehand is usually my weapon but it wasn't working at the beginning, but sooner or later I knew it would come right."
Britain suffered a bad day as both Greg Rusedski and Alex Bogdanovic tumbled out in five sets.
American hopeful and 26th seed Mardy Fish had a good 7-5 6-3 6-2 win over Spain's David Ferrer, while Olivier Rochus beat 27th seed, and Wimbledon semi-finalist, Mario Ancic 7-5 6-2 7-6 (8-6).
But there was sad news for American tennis as Todd Martin announced his retirement after losing to Fabrice Santoro of France.