Reigning US Open champion Marin Cilic came through a titanic tussle with the stubborn Mikhail Kukushkin to book his place in the last 16 of the men's singles at Flushing Meadows.

Kukushkin - looking to make it beyond round three in this event for the first time - triumphed in an opening-set tie-break and served for the second before Cilic seized control of proceedings.

The underdog refused to lie down and came from a break down in set four to force a decider, but Cilic ultimately prevailed 6-7 (5-7) 7-6 (7-1) 6-3 6-7 (3-7) 6-1 after four hours and 10 minutes.

Early breaks were exchanged before Cilic moved 5-3 ahead in the opener, only to slip up when serving for the set.

Kukushkin capitalised by winning the subsequent tie-break, despite enduring a moment to forget at 6-4 up when he opted to leave a lob from his opponent that dropped in.

An outstanding lob from the world number 56 then forced two break points on the Cilic serve in game six of set two, with the Croatian unable to save the second.

Yet Kukushkin then dropped serve when leading 5-3 and also spurned two set points when Cilic served in the 12th game, prompting a second breaker that the reigning champion took with ease.

With the momentum having shifted, it was a case of third time lucky for Cilic in set three as he broke for a 5-3 advantage having missed opportunities in each of Kukushkin's two previous service games.

Kukushkin looked to be down and out when he dropped serve again at the start of set four and received treatment on his left foot, but the Kazakh demonstrated impressive resolve to hit back before coming through another tie-break to set up a grandstand finale.

However, having worked so hard to stay in the match, Kukushkin ran out of gas in the final set as a relieved Cilic finally made it through.