Novak Djokovic is back at world number one after beating Alexandre Muller in straight sets and Iga Swiatek began her title defence by dropping only one game against Rebecca Peterson.
Britain’s Lily Miyazaki made a mark on her Flushing Meadows debut to reach round two.
Here, the PA news agency looks back at day one at the US Open.
Pic of the day
Former first lady Michelle Obama joined a ceremony to honour former champion and equality campaigner Billie Jean King, and celebrate 50 years since the US Open offered equal prize money to men and women.
Match of the day
Coco Gauff came from a set down in a thriller under the lights on Arthur Ashe against German qualifier Laura Siegemund. The American teenager, seeded sixth, eventually came through 3-6 6-2 6-4.
Shock of the day
Holger Rune tweeted a map of the Flushing Meadows site to highlight his frustration at being shoved out on Court Five. The Danish fourth seed’s irritation was clear as he slumped to a four-set defeat to Spaniard Roberto Carballes Baena.
Stench of the day
It’s a hard court, not grass, but eighth seed Maria Sakkari complained to the umpire about the smell of “weed” wafting through the air during her surprise defeat by Rebeka Masarova.
Brit watch
Lily Miyazaki branded her US Open debut “surreal” after winning her first match at a grand slam.
There were echoes of Emma Raducanu after the 27-year-old qualifier, Britain’s sole representative on day one, beat Russian Margarita Betova 6-3 6-3.
“It’s huge for me, I think,” said Miyazaki. “Qualifying was also, like, obviously a huge confidence booster, but winning at the main draw, it just feels a bit surreal.”
The world number 199 may be unlikely to emulate Raducanu’s fairy-tale title win two years ago, but she still secured a near-£100,000 pay day and a high-profile second-round match against Olympic champion Belinda Bencic.
Fallen seeds
Women: Maria Sakkari (8), Veronika Kudermetova (16), Anhalina Kalinina (28), Elisabetta Cocciaretto (29).
Men: Holger Rune (4), Felix Auger-Aliassime (15), Lorenzo Musetti (18), Alexander Bublik (25), Sebastian Korda (31).
Who’s up next?
Day two sees the other six British hopefuls begin their campaigns. Former champion Andy Murray will be on the Grandstand Court against Frenchman Corentin Moutet. Cameron Norrie, Dan Evans, Jack Draper, Jodie Burrage and Katie Boulter are also in action along with defending champion Carlos Alcaraz.