Isner, playing in his first ATP match since losing in the quarterfinals at the US Open in September and becoming a father later that month, never faced break point throughout the 2-hour, 27-minute affair. He struck 31 aces in the victory and next faces another American, Tennys Sandgren, who downed Germany’s Oscar Otte 7-6 (4), 3-6, 6-3.

Second-seeded Italian Fabio Fognini had a much easier time in advancing, defeating Slovakia’s Lukáš Lacko 6-4, 6-4. Fognini next faces South Korean sixth seed Hyeon Chung.

A pair of upsets rounded out Thursday’s action. Latvian qualifier Ernests Gulbis upended seventh-seeded Canadian Denis Shapovalov 6-2, 6-4 and moves on to face fourth-seeded American Jack Sock. Germany’s Philipp Kohlschreiber rallied past eighth-seeded Spaniard Fernando Verdasco 4-6, 7-5, 7-6 (5) and next plays Greek third seed Stefanos Tsitsipas.