Top-seeded Alexander Zverev kept his bid for a first US Open title on track with another gritty five-set victory over Quentin Halys on Thursday.

World No. 2 Zverev laboured until 2:15 am Friday at Arthur Ashe Stadium to shake off 52nd-ranked Frenchman Halys 6-4, 4-6, 7-6 (7-3), 6-7 (3-7), 6-3. The four-hour 33-minute marathon followed his wild first-round five-setter against 89th-ranked Lorenzo Sonego that kept Zverev at it until shortly before 2 am on Wednesday.