The top-seeded American needed six match points to finish off Tomic for his first victory since last year’s Paris Masters. He followed that tournament by dropping all three matches in his first appearance at the season-ending ATP Finals and was 0-2 to start 2019, including a first-round loss at the Australian Open.
Isner, ranked No. 9, became the No. 1 seed on Long Island when Kevin Anderson was forced to withdraw with an elbow injury.
Isner next plays No. 7 seed Jordan Thompson of Australia, who beat American Christopher Eubanks 4-6, 6-1, 6-4. Paolo Lorenzi of Italy got by Ryan Harrison of the U.S. 4-6, 6-4, 6-4 in the other second-round match.