Andy Murray halts his service action to complain about noise from the Argentine section. He wallops down the serve in anger to bring up 40-15.

A rocket ace. 40-30.

One more to go.

Andy Murray's backhand is swallowed by the net.

Three break points and 0-40.

Is this the beginning of the end?

Andy Murray's forehand loses a wrestle with the net cord and Juan Martin del Potro has 0-30 on the Scot's serve.

This is big.

Still no nearer knowing who is going to take this opening singles rubber.

Delpo batters on.

Four hours forty-three minutes on the clock.

Image source, PA

Andy Murray makes a jaw-dropping eyeball-popping physics-defying crosscourt forehand to make it to 30-30.

It was whipped off his shoelaces and dipped down right into the apex of base and sideline at the back of the court. All at full pelt and stretch.

That is the sort of thing that the Brit is having to come up with to balance out the flow of free points off the Del Potro serve though.

Another massive slug from the Argentine for 40-30.

But Murray has sneaked his way to deuce,

Rhosyn Morgan-Davies: This feels like it should be the final!

John Inverdale
BBC commentator in Glasgow

That is sensational. The crowd know it and Andy Murray knows it too.

John Lloyd
Former GB Davis Cup captain on BBC Two

It has been a superb match, two great competitors. It is the first match of the Davis Cup tie and you have a match like this!

What a treat for everyone watching this.

Like a boss.

Andy Murray comes through the slings and arrows of Juan Martin del Potro's jumbo-sized ground game and seals the game with a textbook net raid and forehand volley.

Andy Murray scrapes break point back of the table with a missile serve down the middle and out of reach.

"Let's go!" he shouts.

From 40-0 up this has transformed into a possibly pivotal game.

Image source, PA

Andy Murray with a flimsy, flaky, but absolutely perfectly calibrated drop-shot moves onto 30-0.

A brute of a serve move him to 40-0 and the brink.

That is the ugly face of the Murray dropper though. An ambitious baseline slice flops into the middle of the net. 40-30.

Double fault and deuce!

Hit play below to see a tense exchange between Murray and Del Potro result in a delicate little drop volley by the Argentine to take this epic match into a deciding set.

John Lloyd
Former GB Davis Cup captain on BBC Two

This crowd are not letting them be tired. 

Murray looks out on his feet some times and then the crowd gets behind him and he runs like a gazelle out there.

"Si!"

Juan Martin del Potro slots away a forehand volley to close out the game.

This might be last man standing by the end. Marathon tennis and both players are showing the strain.

Andy Murray, shoulders heaving, stooping to regain his breath, has just managed to live with the Del Potro demolition ball groundstrokes and save game point.

But the sledgehammer serve brings up another for the Argentine...

Andy Murray roars in frustration.

Love-fifteen up with a second serve to look at, he slaps weakly into the top of the net.

That was a chance to really get the crowbar into this service game.

Into a rally at 30-15 down and Murray chasing hard to keep up with a pummelling forehand hammerblows from the other end.

Del Potro eventually dents him out of shape.

With some careful courtcraft, Murray sneaks up court to take another point 40-30.

And deuce as Del Potro dumps a backhand into the net under no pressure!

Image source, Getty Images

John Lloyd
Former GB Davis Cup captain on BBC Two

Not to be unsportsmanlike but this is a nice sight for Andy Murray.

When you see your opponent tiring you love that.