Andy Murray has admitted his first-round US Open clash with Nick Kyrgios was difficult in tough conditions at Flushing Meadows this morning.

Murray defeated the Australian 7-5 6-3 4-6 6-1 to progress to the second round, and the Scotsman admits that the physicality of Kyrgios makes him a tough opponent.

Speaking to ESPN after the game, Murray said: "It was tough, I had to do a lot of defending tonight and a lot of running in very humid, tough conditions.

"He's unpredictable, he can play all the shots, he serves extremely well. He's a fantastic athlete, big guy as well - he covers the court extremely well and it's tough to get it out of his stride zone.

"I just fought hard, mixed it up and managed to get through."

Murray will face Adrian Mannarino in the second round on Thursday, September 3.