Renata Zarazua, the only Mexican player in the US Open main draw, pulled off a stunning upset by beating sixth seed Madison Keys in the first round.
Players from the Philippines and Hong Kong will be on the schedule for the second round of a Grand Slam for the first time this week, as the U.S. Open sees the impact of an increasingly global game.
Tenth seed Lorenzo Musetti rallied from a set down to beat Frenchman Giovanni Mpetshi Perricard in the first round of the US Open on Tuesday even as Carlos Alcaraz mauled big-serving American Reilly Opelka and veteran Venus Williams made an emotional exit.
Djokovic tamed local favourite Rinky Hijikata 6-3, 6-3 in what was the top seeded Serbian's first tour-level singles match since October.
Colombia's Camila Osorio pulled out a 7-6 (5), 6-7 (2), 7-5 win over Russia's Veronika Kudermetova, and Italy's Martina Trevisan beat Mexico's Renata Zarazua 6-4, 6-3.
Carlos Alcaraz will be backed to extend his winning run at the Grand Slams to 16 matches following triumphant French Open and Wimbledon campaigns.
IMAGES from Day 1 of the Wimbledon Championships, at the All England Lawn Tennis and Croquet Club, London, on Monday.
Images from Day 4 of the French Open, at Roland Garros, in Paris.