Serena Williams is playing in the first night match on Arthur Ashe Stadium, just as she was on the opening day of the tournament. She plays No. 2 seed Anett Kontaveit of Estonia.
Williams began what could be the final tournament of her career by beating Danka Kovinic 6-3, 6-3 on Monday night.
Top-ranked Daniil Medvedev, the defending men's champion, follows Williams against Arthur Rinderknech of France.
Early starters Wednesday included third-seeded Maria Sakkari, a semifinalist in Flushing Meadows last year, and No. 5 seed Ons Jabeur, the Wimbledon runner-up. Opening-round matches in men's and women's doubles were also on the court.
Past champion Andy Murray, 18-year-old Coco Gauff and Wimbledon runner-up Nick Kyrgios were also scheduled for day singles action.