Kei Nishikori stepped up his comeback by reaching the New York Open quarter-finals, but fellow seed John Isner exited the tournament.

Japanese star Nishikori is back on the ATP World Tour, having withdrawn from last month's Australian Open as he recovered from a wrist injury that forced him to miss the end of 2017.

And fifth seed Nishikori, who won a Challenger Tour title in February, rolled on with a routine 6-2 6-4 victory over Russian Evgeny Donskoy on Wednesday.

Nishikori showed no signs of that wrist problem, firing down seven aces, winning 83 per cent of his first serves and 85 per cent on his second without facing a break point throughout the contest.

Next up for Nishikori is Radu Albot, who sent giant American and third seed Isner packing from the inaugural event.

Isner was upstaged by Moldova's Albot 7-6 (7-5) 3-6 6-3 in the second round midweek.

Despite tallying 28 aces to Albot's one, Isner crashed out as he lost his third consecutive first-round match this season, including the Australian Open.

Adrian Mannarino – the fourth seed – was leading 6-7 (5-7) 7-5 4-1 when his German opponent Peter Gojowczyk retired due to injury, while Jeremy Chardy lost 7-5 7-6 (7-5) against Adrian Menendez-Maceiras.