US Open 2014: Andy Murray beats Andrey Kuznetsov in third round

Murray won 70% of points on his first serve

Andy Murray moved into the last 16 at the US Open with a four-set win over Russia's Andrey Kuznetsov in New York.

The 2012 champion won 6-1 7-5 4-6 6-2 with a patchy performance on the Louis Armstrong Stadium, the second show court at Flushing Meadows.

It had been the scene of a worrying attack of cramp in Murray's opening match, but he appeared to come through round three physically unscathed.

The Briton still found Armstrong an uncomfortable venue though, as double faults and unexpected errors allowed his opponent a way back into the match.

Murray snuffed out any sense of a real crisis by dominating the fourth set, and he will play French ninth seed Jo-Wilfried Tsonga in round four.

"The first couple of sets were pretty good and then I started a bit slow in the beginning of the third," said Murray.

"He gained confidence from that and he definitely started hitting the ball better in the third set."

Murray's form has been uncertain throughout a year in which he has failed to win a title, and there were more signs of that fragility with lapses in the second and third sets.

He faced more pressure than he would have liked on serve, up against 10 break points and dropping serve four times, but Murray dominated the baseline exchanges and Kuznetsov's own serve was not potent enough to keep the Scot at bay.

Kuznetsov helped the world number nine out early on with some nervous errors as he dropped serve immediately.

Murray's coach, Amelie Mauresmo, kept a close eye on the action courtside

When Murray broke for the third time with a rasping forehand winner at the start of the second, the result already seemed beyond doubt.

It took 46 minutes for Kuznetsov to register his second game, which made it all the more surprising that the Russian was still on court after two hours and 35 minutes.

Murray brought him level at 4-4 in the second set with a double fault on break point but rectified the situation by powering away a forehand to restore his advantage at 6-5, and giving a loud "Come on!" when an ace brought him the second set.

It was at two sets up that the problems began for Murray in his first-round match against Robin Haase, and there were worrying signs of a repeat when he slipped 4-1 down in the third.

The former Wimbledon champion was again able to step up his game to draw level at 4-4 but, after Kuznetsov fended off two potentially decisive break points to stay alive, the Russian was then gifted a route back into the contest.

Serving to stay in the third set, Murray missed with a forehand, blazed a drive volley wide and then, on set point, double-faulted.

He made amends with some impressive play in a one-sided fourth set, but there was another loose service game at 4-1 before Murray wrapped up victory with a sharp backhand volley.

"Today it could have been a bit quicker if I got that break point at 4-4 in the third set," said Murray.

"But each time I had a slip, I did a decent job of getting myself back into the sets, getting a break straight away.

"Even when I got broken at the end of the match, I broke the next game. When I was down 4-1 in the third set, I got myself back into the set.

"That's really what you need to do. You need to give yourself opportunities in every set and in matches."

The Louis Armstrong stadium holds 10,103 people and it was near capacity for Andy Murray's match

Murray's opponent, Kuznetsov, won the junior title at Wimbledon in 2009

Murray had never played Kuznetsov before in his career