Defending champion Andy Murray was forced to grind out a victory over Denis Istomin to set up a US Open quarter final encounter with Stanislas Wawrinka on Thursday.

The British number one was forced to come from a set down to beat his Uzbekistani opponent 6-7 (5-7) 6-1 6-4 6-4 as he struggled to assert himself on a windy evening in New York where he was also irked by a selection of line calls before sealing the win in three hours and seven minutes.

Tuesday's win leaves the Scot to face ninth seed Wawrinka for a place in the last four, still on course to retain his US Open championship in the year's last major.

Two double faults helped Istomin taker a 5-3 advantage in the opening set before he handed the break back to the Scot who forced a tie break. Murray then took his own 5-3 lead in the set's decider but relinquished his advantage through another double fault and a backhand error to hand his opponent the first set.

The Brit would respond in swift and ruthless fashion in the second set, breaking in the second game as he went on to restore parity in the contest.

Murray also broke early in the third set before letting his lead slip once again. But as the contest threatened to evolve into a dogfight at 3-3, Murray's experience prevailed again as he broke in the seventh game before taking the set.

Tied at 4-4 in the game's fourth set, Murray capitalised when Itsomin, caught cold by a gust blowing through the Arthur Ashe Stadium, was left isolated as Murray struck a fine forehand volley on match point to seal the victory.

"I wanted to just try and get through the match," Murray told BBC Sport. "In the end it was difficult conditions. It was extremely windy.

"With the way he plays, he hits the ball pretty big and flat on both sides, strokes pretty low, hard at times to control. He made it very difficult for me.

"With the way the third set ended up going, I was just very happy to get it done because he had chances at the end of the third set to go ahead."