Kuznetsov hoicks a forehand return wide and Murray moves 30-15 ahead after his opponent sends an outside edge into the stand. Kuznetsov outlasts Murray for 30-30 but puts a return long for 40-30 and tugs a backhand wide to hand Murray the game.

A change of racquet for Kuznetsov as one of his string dampeners goes missing. Murray makes it 30-15 courtesy of a big forehand return but an attempted forehand winner misses the sideline. Kuznetsov wraps up the game with an ace down the middle.

Double fault from Murray makes it 15-30 but he finds a wicked, arcing forehand for 30-30. Murray converts a backhand volley for 40-30, despite his legs not being where they should have been, but follows that with another double, his fourth of the match. Murray finds a first serve and puts away the resulting forehand before Kuznetsov skims the baseline with a return for deuce. Murray nets with a backhand and he doesn't look right out there. Lots of strange, sudden jerks, as if he's cramping up again. And that's a break for the Russian.

Game, set and match Novak Djokovic. The Serbian number one sees off Sam Querrey in straight sets as he wins 6-3 6-2 6-2.

Murray misses a very makeable return off a second serve before spraying a backhand long for 40-15. Murray hooks another return long and that's a relatively straightforward hold for the Russian.

Miles Maclagan
Former coach to Andy Murray on BBC Radio 5 live Sports Extra

"The most worrying time for Andy is when there is no emotion. He needs something to fire off. When there is no energy that is when he struggles."

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The Louis Armstrong Stadium holds 10,103 and is pretty full of tennis fans right now, including these Andy Murray supporters.

Murray shovels a backhand wide for 15-15 before sending down a battery of gigantic forehands for 30-15. Kuznetsov hits back with a crackerjack forehand return before Murray finds a big first serve for 40-30. And that's a hold as Kuznetsov bunts a return long.

Murray moves into a 0-30 lead but Kuznetsov chisels his way back into the game. Murray forces a break point but Kuznetsov saves with a wrong-footing forehand. The Russian prods over a backhand smash for the advantage and dredges up some more big hitting to hold.

Kuznetsov matches Murray blow for blow in that rally, makes it 15-15. But Murray thunders down an ace out wide for 40-15 before wrapping up the set with another thumper down the middle. Murray faltered towards the end of that set but once he was upright again he got back to bullying.

Piers Newbery
BBC Sport at Flushing Meadows

"Murray has developed a knack of turning winning positions into unexpected scraps over the US hard-court summer, and it happens once again as he lets Kuznetsov into a match that seemed way beyond the Russian. Having dominated for an hour, Murray was also playing with fire by offering up seven break points. The sun returns and the heat rises - Murray could yet be in for another testing afternoon on Armstrong. "

Only 32% of second serves won by Kuznetsov and Murray has stolen a 15-40 lead in this game. What a forehand return that is from Murray, he almost put his back out hitting that. Normal service resumed, Murray to serve for the set.

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Plenty of cloud cover now which is making things a little bit cooler out there. Murray serving to stay in the set and he races into a 40-0 lead behind some big deliveries. Kuznetsov fires a backhand return wide, easy hold for Murray.

Murray takes the first two points of the game before the Russian hits back with a crackerjack backhand down the line. Oh! I! Say! Shot of the match, a ripsnorting forehand winner down the line, on the stretch, from Kuznetsov. Murray gets a sniff of a Kuznetsov second serve but dumps his return into the net. The tennis gods have switched Murray's gas off and he's barely simmering on the hob.

Nice work from Kuznetsov there, showing good variety to move into a 0-30 lead. Murray slams down an ace for 15-30 only to net with a backhand and hand his opponent two more break points. Murray pulls out another ace to save the first before pulling out another plum for deuce - Kuznetsov got it back but Murray followed up with a flying forehand winner. Murray berates himself after finding the net with a sliced backhand and here's a break, courtesy of a double fault.

Over on Arthur Ashe, it's all too easy for Novak Djokovic. The Serbian world number one goes two sets up against American Sam Querrey and surely a place in the fourth round is just a matter of time?

That's a love service game from Kuznetsov, which must be a merciful treat at this stage in the match...

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Murray pulls his rival hither and tither before putting away a cross-court forehand for 15-0 and makes it 30-0 courtesy of another thumping forehand. Murray pulls out another big first serve and wins the game to love. Kuznetsov is going to need a big hug from his woman after this, whoever that may be.

The wriest of smiles of Kuznetsov at the start of the game, as if to say: "When they said he was good..." But the Russian packs a punch into that wiry frame of his and here's a crunching backhand for 40-30. Murray crowds another Kuznetsov second serve for deuce before the Russian puts away an overhead. Nice hustling from Kuznetsov, and eventually he makes Murray buckle with another well-directed smash.