Andy Murray - with hours of court time on the clock, muscles aching, fatigue in the brain - is still playing somewhere near his tip-top best.

A hold to 15 is topped off with a jumbo-sized inside out forehand.

Forget hanging on, it looks like Britain's number one is finishing the stronger.

Image source, PA

That was a kamikaze, self-inflicted break of serve from Guido Pella.

He screws a backhand a smidge wide on the first break point to slip behind in the third set.

He dashes his racquet to the floor in frustration because he knows that he now has to do something that he has not got within a point of doing so far - breaking Andy Murray. 

Guido Pella finds his mark.

A roundhouse backhand down the line brings up 40-15.

Andy Murray wrote that one off as a lost cause, rather than sprint and risk it.

It is like Murray's injury has got into Pella's head a little too though.

Under pressure to move the Scot about and play a more aggressive game, he twice flops long to hand Murray deuce from 40-15 up.

Jamie Baker
Former GB Davis Cup player on BBC One

Murray does look just slightly hesitant.

Between points, Andy Murray is creaking, walking like a man in ski boots.

When the ball is in play though, his movement looks good enough, if not the warp speed burst that we are used to.

He is going for the jugular early in rallies though to try and keep the points short.

That, backed up by some accurate serving, sees him through to 30.

Jamie Baker
Former GB Davis Cup player on BBC One

Image source, Reuters

I think I might have heard Andy mouth that he has pulled a muscle.

Andy Murray jogs back onto court.

A hint of a hobble perhaps, but he is determined to get the show back on the road.

Let's see how this goes.

Jamie Baker
Former GB Davis Cup player on BBC One

Pella will get an inkling.

A drastic change of tactic, like the use of the drop shot, will come in if it is a serious injury.

The wait goes on in the Emirates Arena.

Guido Pella is stretching and lunging like Mr Motivator.

The British backroom staff look glum.

The Argentine fans less so... 

This is not looking too clever at all for Andy Murray.

Replays show him pulling up sharply and immediately mid-rally after feeling something in his groin/upper leg.

As he returned to his stool, he was giving his own amateur diagnosis to captain Leon Smith.

From my lip-reading, it didn't look very optimistic.

Uh-oh.

Trouble up mill.

Andy Murray appears to have tweaked something in his right thigh.

He folds out of the game to love , barely chasing Pella shots.

The trainer is on to work on the muscle.

Image source, Getty Images

Andy Murray puts up a steepling moon ball defence at 15-15, but is confounded by one of the rafters on the Emirates Arena roof.

It deflects his ball out of court and suddenly there is a bit of pressure at 15-30.

Murray stamps out the danger like a Cossack dancer on overtime. 

Three quick commanding points and he is ready for another tilt at the Pella tee-off.

John Inverdale
BBC commentator in Glasgow

That must have been the least 'in' of all tennis balls in the history of the game.

Guido Pella hangs onto his serve by the skinniest of margins as his forehand whiffs the tiniest snip of line on break point.

If that had been out, would it have been curtains.

It might not have been far off.

Andy Murray slots a precise backhand down the line to ask a 30-30 question of Guido Pella.

The Argentine's reply is blunt, but eloquent. A slammed cross-court winner.

A scruffy backhand into the net though allows Murray to bring up deuce.

Blood in the water?

Andy Murray could not land a first serve, but it didn't matter.

Guido Pella dumps a flimsy backhand into the net and the Proclaimers are on the PA system.

Two sets to the good.

If Pella could tap out he might. There is no submission, but capitulation is possible in the third.

Image source, Getty Images

A double fault on the first set point keeps the isotonic on ice and send the game to deuce.

But Andy Murray has a second chance.

Can he locate a first serve?

Guido Pella is being made to work hard even for his bread-and-butter service games.

He gratefully scampers forward to slam hard into the court floor and hold to 30.

 At the changeover, Pella is in animated discussion with captain Daniel Orsanic, but I'm not sure that a brain trust of Nobel Prize winners could come up with a tactic that is going to turn around this one the way that Murray is playing at the moment.

Their best hope is that the British number one comes suddenly and significantly off the boil.

Image source, Getty Images

In terms of total points in this match, Andy Murray has won 55 to Pella's 38.

The gulf feels greater.

Murray skips through a love service hold like Maria Von Trapp.

I'm not sure whether it is the best tennis that he has played this weekend, given the differing standards of the opposition, but it certainly his most commanding performance.

Miles Maclagan
Former British Davis Cup player on Radio 5 live sports extra

It really has been very, very, solid from Murray this afternoon. 

We can see the difference in levels between a very, very, good pro and a world class athlete.