Serena Williams showed no sign of the shoulder injury that disrupted her US Open preparation as she dismissed Ekaterina Makarova in straight sets.
The top seed faced a tricky first-round opponent in Makarova, Russia's world number 29, but won 6-3 6-3.
Williams, 34, will monitor how her shoulder reacts before her second-round match against Vania King.
"I'll have to wait until tomorrow to see - I haven't been able to play that much since Wimbledon," said Williams.
"Every day I'll just see how it goes."
Williams had played just three matches since winning Wimbledon, but impressed against 2014 semi-finalist Makarova in the night session.
"I love coming out here in front of this New York crowd, it's super special," said the six-time champion, chasing an open-era record 23rd Grand Slam singles title.
"I got off to a really fast start - I wanted to get some momentum."
Venus Williams, seeded sixth, survived 63 unforced errors to beat Kateryna Kozlova of Ukraine 6-2 5-7 6-4.
Fourth seed Agnieszka Radwanska and fifth seed Simona Halep lost four games between them as they progressed, while leading names Stan Wawrinka, Kei Nishikori and Juan Martin del Potro went through in the men's draw.
Meanwhile there was an upset in the men's draw as 12th-seeded Belgian David Goffin was beaten 4-6 7-5 6-4 6-0 by 19-year-old American qualifier Jared Donaldson.
Australia's Bernard Tomic apologised after making lewd comments to a spectator - the world number 19 insisted he was "baited".