Seventh seed Kei Nishikori overcame a spirited display from Bradley Klahn to book his place in the third round of the US Open with a 6-2 4-6 6-3 7-5 win.

The Japanese player was 5-1 up in the fourth set and had four match points before eventually overcoming the world number 108.

The 2014 finalist eased into a one-set lead and was 4-2 up in the second before Klahn fought back to level.

Nishikori reasserted control to secure victory in two hours and 43 minutes.

The 29-year-old will now play either 31st seed Cristian Garin of Chile or 20-year-old Australian Alex de Minaur in the next round.

Elsewhere, Croatian 12th seed Borna Coric withdrew from the competition with a lower back strain before he was due to play Bulgarian former world number three Grigor Dimitrov.

The 22-year-old, who reached the fourth round last year, tweeted: "The last couple of months were really tough because of the injury I had. For an athlete, the worst thing that can happen is an injury in the middle of the competition.

"It is never easy to withdraw but at this moment, my body is telling me to stop and assess the situation. So as hard as this decision is, I think it is smart in the long term."