Juan Martin del Potro - the 2009 champion at Flushing Meadows - is through to the fourth round with a highly impressive 7-6 (7-3) 6-2 6-3 win over David Ferrer.

Dominic Thiem is up next for the Argentine, who is now ranked 142 after undergoing a series of wrist injuries. That match will be a doozie.

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David Law
Radio 5 live sports extra commentator

Murray's body language shows that he is fed up with the way things are going. There's an anger in the way he's playing but he's not setting these points up as well as he might do. 

There's also a little heaviness in his legs and he looks a bit off balance at times. 

He's making things hard for himself.

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And Paolo Lorenzi follows up his break with a hold to love.

He is chucking the kitchen sink at his groundstrokes and Andy Murray is struggling to work out how to curb the Italian's enthusiasm.

Hang on, are you sure this is the right script?

I thought this was the point were the plucky underdog settled on the story he had for the grandkids and bowed out sharpish.

Instead Paolo Lorenzi breaks Andy Murray to love, finishing the job with a vicious dipping pass.

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SJ McNab: This Italian bloke Murray is playing has the oddest serve. It's like he's a baseball pitcher?

There is a lot of leg bend in there. The backwards baseball cap is helping his impression as well. Which reminds me. Check out this video of John McEnroe's first pitch at a New York Mets game., external A bullet.

With that mongrel of a first set behind him, Andy Murray is starting to fling those tree-toppling forehands.

Massive lumberjack swings take the first point of the set against the head before a blind swat over his shoulder as he chases back moves the Scot 0-30 up.

A devilish dropper, sliced off the forehand, brings up break point at 30-40.

Converted in clinical style as Murray rushes the net and punches away the forehand volley into open court.

Paul Newman
Tennis correspondent for the Independent on BBC Radio 5 live sports extra

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That's a great way to end the set with a superb return but it was a set full of unforced errors. I suspect he couldn't quite work out how to go about the match. He was going for his shots too quickly.

If there was any way Lorenzi  was going to win that was it. I would think Murray will close it out quite quickly now and let's hope that Murray has got his bad set out of the way for the tournament now.

Andy Murray takes out his aggression and frustration after an eyesore of a first set, lasering a death-ray return right up onto Paolo Lorenzi's toes.

The crowd audibly omph.

Lorenzi just about saves his tootsies. But it is at the expense of the set.

Andy Murray tugging for home now, stretching Paolo Lorenzi out of shape to move to within two points.

Make that one as Murray smears through the whitewash. 

Three set points.

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Andy Murray clatters away a return, as short and compact as a Tyson hook to pull a mini break ahead.

Paolo Lorenzi holds serve on his second attempt though.

Paolo Lorenzi with a second serve to attack, pumps long. A waste for the Italian.

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A 27th (twenty-seventh!) unforced error from Andy Murray and we are back on serve in the shoot-out.

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Paolo Lorenzi chasing like a labrador on heat, but Andy Murray finally finds the killer punch and he wallops away an overhead smash.

Andy Murray claws back to parity as Paolo Lorenzi follows him down the gurgler and into the gauze.

Russell Fuller
BBC tennis correspondent in New York

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The timing is lacking so frequently in Murray's shots. It's very odd to see Murray doing that. But well done Paolo Lorenzi, especially after the gruelling match he had in the second round, to play this well.

And Andy Murray whiffy form continues as he plants into the net and coughs up the mini-break on the very first point.

Russell Fuller
BBC tennis correspondent in New York

I've not seen every match but this is quite possibly the worst set Murray has played since he hit the clay in Rome.

Andy Murray chases down a mid-court bounce, clambers into a backhand return, but it is too little too late to claw Paolo Lorenzi back from 40-0 up.

Into a tie-break shoot-out.

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Paul Newman
Tennis correspondent for the Independent on BBC Radio 5 live sports extra

Lorenzi will not have experienced anything like this before, facing the world number two on a stadium like Arthur Ashe.

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Andy Murray has a little mid-game rant up towards his box, accusing them of having "no energy".

Ivan Lendl remains perfectly impassive for a delicious moment, before whispering something behind his hand to fellow coach Jamie Delgado.

Delgado giggles. Ivan Lendl is nobody's cheerleader.

Murray gets through the game without the poms-poms and pep rally.