Kei Nishikori has progressed into the third round of the US Open courtesy of a four-set victory over Karen Khachanov at Flushing Meadows.

The world number seven overcame a rain delay to eventually win 6-4 4-6 6-4 6-3 and set up a third-round meeting with Nicolas Mahut.

Khachanov earned control of the opening set when he claimed the first break to move 3-2 in front, but Nishikori responded in kind immediately to force the set back on serve.

The Japanese number one then powered into a 40-0 lead at 5-4 up to put himself on the brink of claiming the first set, but he needed all three of his set points to eventually take it.

It was a solitary break that proved decisive in the second set, and this time it went to Khachanov as the Russian moved into a 5-4 lead before serving out to level things up.

It was a similar story in the third as once again the set looked destined for a tie-break until the closing stages, when this time Nishikori broke in the final game to move 2-1 ahead.

Nishikori, a finalist at Flushing Meadows in 2014, was forced to save two break points in the opening game of the fourth, but then lost three games on the bounce as Khachanov threatened to force a decider.

However, Nishikori responded with a five-game streak of his own to wrap up the victory and book his place in the third round.