Andy Murray buys a pass back into the game at 30-0 down with a dipping forehand,fizzing with topspin.

A brutal backhand return, slapping a wide serve away for a winner at a vicious jagging angle makes it 30-30.

A leaping swish of a forehand brings up break point after Murray soaks up the best that Pella can throw at him.

Murray missed six break points in the previous game. He only needs one this time.

Pella bumps long and is surely torpedoed in this second set at a double break adrift.

David Law
Radio 5 live sports extra commentator

That smash was Jimmy Connors-style from 20 years ago.

Andy Murray wallops down a fifth ace of the match to hold to 15 after a neat pirouette smash on the previous point.

That serve looks locked up as tight as Fort Knox.

Jamie Baker
Former GB Davis Cup player on BBC One

How hard did Pella have to work to hold serve? 

That was a seriously tough game but in the context of the match, how much has that taken out of him?

As good a player as Pella is, it just looks like Murray has another gear.

Great Britain captain Leon Smith looks like he is living every ebb and flow of this marathon game.

Guido Pella has now saved six break points.

And he closes it out as he pats away a winning volley!

A pat on the head from Argentine captain Daniel Orsanic and it felt like this could be an important psychological game in this match.

Image source, Getty Images

Andy Murray seems to have a little white-line fever, struggling to get through the final hard yard in this game.

 A couple of errors, a big serve and three more break points have been pulled out of the fire by Guido Pella.

A sixth is coming up through...

Guido Pella is foxed by a viciously dipping pass that divebombs on his toes for 30-30.

 The Argentine is looking a little sea-sick out there amid the Barmy Army's swaying, hollering support.

A double-fault and a break point.

Murray nets that one, but here comes another.

First serve missed by Pella. Into a rally, Pella making the running, Murray probing the angles, but into the net once more from the Briton.

Pella is wobbling, can Murray prod him over the edge?

Jamie Baker
Former GB Davis Cup player on BBC One

That was another huge second serve from Murray.

I wonder if that is another move for tactical reasons because of Pella's returns or Murray has said 'I want some shorter points today.'

I have never seen him hit second serves so big.

Andy Murray is mixing it up like Tom Cruise in Cocktail.

A slug of serve accuracy, a splash of groundstroke power and a cheeky dash of drop-shot.

It is too heady a brew for Guido Pella so far.

Murray backs up the break with space to spare.

Amy: @andy_murray is my favourite sportsman. He must be so exhausted but he just never gives up! So lucky to have him

Luke Guest: Andy Murray is just so inspirational, I'd never walk again after a 5 hour match with Del Potro... he doesn't even look tired!

Jiten Chandarana: Murray at 62% first serves in, compared to 50% against JMDP. Makes life a lot easier for Andy.

Andy Murray is chomping at the bit.

He looks like a man eager to swap the job of on-court great hope for off-court head cheerleader.

Love-thirty becomes 30-40 and a break point as he runs down Guido Pella's drop volley and swats past the Argentine.

 A sublime passing shot cuts off Pella as he comes into the net. 

Murray roaring, the Emirates Arena on its feet, this belief is spreading.

Image source, Getty Images

Jamie Baker
Former GB Davis Cup player on BBC One

How many times in the Del Potro match did Murray's serve come to the rescue?

It was the same there.

A second-serve winner and the third ace of the match snuff out the Argentine resistance.

Andy Murray has been making the gap in pedigree and experience show so far.

You wouldn't bet against a second-set dip though. Andy Murray's Davis Cup liaisons are rarely straightforward affairs.

Image source, Getty Images

Andy Murray sets a few nerves on edge as he slips to 15-30 down.

That serve is a crutch to lean on in such situations though.

A couple of bona-fide bombs take the next two points and move him to the brink at 40-30.

Not so fast says Guido Pella. A forceful forehand down the line and a thrashing volley bring up deuce.

Guido Pella's serve has been tight and tidy since been burgled just the once in this set.

Another hold to love.

Andy Murray will serve for the opener next. And he may have been keeping his powder dry for that.

Andy Murray is having more success when he keeps his patience, builds the point and waits until he has the chance to move up the court before going for the winners.

He is a whisker wide as he unleashes from the back of the court looking for the clean kill.

He challenges optimistically. HawkEye turns him down politely. 

Thirty-all.

Murray clambers into a cross-court backhand from well inside the baseline. That's better.

And he then skitters in to swat down a smash and close out the game.

Guido Pella notches up a hold to love.

Argentina captain Daniel Orsanic is a man under pressure.

If his side fluff this tie after going 2-0 up, there will be a full, public and unpretty inquest back in Buenos Aires.

He claps enthusiastically as the balls swap ends.

Image source, Reuters

If this is Andy Murray with his batteries run down, Guido Pella would not like to see the fully charged, fully rested version.

The British kingpin is carving though his man so far. A whipsmart hold and he has clear blue water with only 18 minutes on the clock.