Andy Murray has admitted that his energy-zapping first two US Open matches could take their toll on his body as the competition progresses.

The Scot and third seed endured a gruelling three-and-a-half-hour marathon to come from two sets down to beat Adrian Mannarino 5-7 4-6 6-1 6-3 6-1 for a third-round place on Thursday night.

Having already secured a four-set win over Nick Kyrgios in the first game, Murray, who is also suffering with a cold, concedes that wear and tear is a possibility.

"In these conditions, obviously it can take its toll later on in the tournament," he told Sky Sports News.

"But unfortunately you don't always have the luxury of winning matches in straight sets. Sometimes you have to fight through if you're not playing your best.

"Thankfully the last three sets were fairly comfortable in terms of the scoreline, otherwise I could have been out there much longer and it would have been very tough to recover from."

Murray faces Brazil's Thomaz Bellucci in the third round later today.