Former champion and world number one Novak Djokovic sparkled under the Arthur Ashe Stadium lights to end a steamy first day that proved more than a little stressful for several of the US Open favourites.
The 2011 champion treated his first-round match against unseeded 22-year-old Argentine Diego Schwartzman like a breezy workout, dominating in all phases with 24 winners including seven aces in a 6-1, 6-2, 6-4 rout.
"I'm very pleased," the Serbian world number one said in a courtside interview after his 97-minute win. "It's never easy to start a U.S. Open smoothly."
Earlier, eighth-seeded 2012 champion Andy Murray fought off cramps to beat Dutchman Robin Haase 6-3, 7-6,1-6, 7-5.
"I felt extremely good before the match, and I did train very, very hard to get ready for the tournament," said Murray. "My quads were cramping, then it started to get to my lats, then my forearms," he added. "I just tried to hang around and at the end I was trying to play without moving my legs much and managed to get through."
However, in an upset on the men's side, twice semi-finalist Mikhail Youzhny of Russia, the 21st seed, fell to big-serving Australian teenager Nick Kyrgios 7-5, 7-6, 2-6, 7-6.