Novak Djokovic and Roger Federer reached the second round while Serena Williams comfortably won her grudge match with Maria Sharapova, 6-1 6-1.
Johanna Konta and Dan Evans kept the British flag flying, but Cameron Norrie and Harriet Dart waved goodbye.
Here, PA looks back at day one and forward to day two at the US Open.
Shot of the day
Federer surprisingly dropped the first set against India's Sumit Nagal, but class told in the end.
Stat of the day
Quote of the day
Shock of the day
Angelique Kerber, the winner here in 2016 and last year's Wimbledon champ, crashed in three sets to unseeded Kristina Mladenovic.
Brit watch
Johanna Konta is safely through while Dan Evans beat Adrian Mannarino in four sets. But Cameron Norrie lost in five to French qualifier Gregoire Barrere and Harriet Dart's campaign ended 6-3 6-1 against Ana Bogdan. British number one Kyle Edmund faces Spain's Pablo Andujar on Tuesday.
Fallen seeds
Men: Fabio Fognini (11), Guido Pella (19), Taylor Fritz (26)
Women: Angelique Kerber (14), Caroline Garcia (27)
Tuesday's order of play
Arthur Ashe Stadium:
Naomi Osaka v Anna Blinkova
Thomas Fabbiano v Dominic Thiem
John Millman v Rafael Nadal
Sloane Stephens v Anna Kalinskaya
Louis Armstrong Stadium:
Stefanos Tsitsipas v Andrey Rublev
Simona Halep v Nicole Gibbs
Anastasia Potapova v Cori Gauff
Aryna Sabalenka v Victoria Azarenka
Steve Johnson v Nick Kyrgios
Court 13:
Kyle Edmund v Pablo Andujar
