Andy Murray's precise serving prompts the crowd into a slap-down gesture as he move 30-15 up.

it is that shot that comes to the Scot's rescue again as he serve-volleys his way out of a sticky corner at 30-40.

Not out of the woods yet though. Deuce.

John Lloyd
Former GB Davis Cup captain on BBC Two

You can see with how these rallies are developing, Murray knows if he keeps going to the Del Potro backhand then Del Potro won't hit many winners.

Del Potro is not getting any cheap points so far. Every point he has to work for.

First blood to Andy Murray and Great Britain.

The third break point is the charm as he converts from 30-40 up to move a break up.

"Let's go Andy, Let's go," chant the crowd.

Vamos indeed.

Andy Murray has got a second career as a surveyor.

The Scot seems to have measured the dimensions of this court to the milimetre as he feathers a third sublime lob of the match over the man mountain opposite to move 0-30 up.

Del Porto into the net - three break points Murray.

Image source, Getty Images

John Lloyd
Former GB Davis Cup captain on BBC Two

It is exhausting already and they have only played one game!

Del Potro can't play a much better game than that and he still didn't win it.

You can see the danger signals from him though, the forehand is just awesome.

Andy Murray stuffs one break point back in his racquet bag with a big serve out wide.

A big snag on the net cord works Murray's way, but Juan Martin del Potro throws a forehand like a gaucho lassooing a headstrong steer.

Nine minutes on the clock and it is all pure-cut quality stuff.

Finally Murray sees of the danger with a shot that deserves to win the game, a tease of a half volley lob over Del Potro that divebombs down plum on the baseline. 

Every single point won by Andy Murray is being cheered to rafters.

The upper reaches of the Emirates Arena get especially drafty as the Scot sends a delicious lob tumbling and top-spinning over the six-foot-six-inch Del Porto and inside the baseline for 30-0.

Del Potro's forehand is a Flintstones-style club of a shot and he pounds his way back to 30-30.

Murray with an ace down the middle for 40-30.

Del Potro hitting hard and deep to take us to deuce.

The standard and tension have started at a suffocatingly high level.

Image source, Getty Images

John Lloyd
Former GB Davis Cup captain on BBC Two

There is nothing like the Davis Cup for a tennis player. 

Perhaps the Olympics is up there but other than that you just don't get this atmosphere. 

In Scotland, the fans have taken it to another level. The players must walk out here and feel a foot taller.

Image source, Getty Images

Image source, Reuters

The atmosphere is jumping.

A rousing rendition of "The Bonnie Banks o' Loch Lomond" from the home fans.

A spirited and rhythmic response from the Argentines.

Andy Murray to serve... 

Image source, Getty Images

Just in case anyone still had any lingering doubts over Andy Murray's commitment to the British cause.

He will miss his paternal grandfather's funeral today to play for his country today.

His brother Jamie is expected to attend the funeral, before teaming up with Andy for Saturday's doubles.

Jamie Baker
Former GB Davis Cup player on BBC Two

This is going to be a great match.

It is fantastic to see Juan Martin Del Potro back at his best.

Due to injury, Juan Martin del Potro is working off only seven months worth of results over the past year so his ranking is wallowing down at 64. 

But that does not reflect how closely they are matched.

Image source, Getty Images

Juan Martin del Porto and Andy Murray have emerged into the Emirates Arena Glasgow to polite and downright raucous receptions respectively .

You won't miss a shot of this weekend's action on the BBC.

BBC Two coverage is up and running. 

You can get that either on the old-fashioned telly box or on your new-fangled digital device - just have a poke around at the top of this page.

There is also coverage of BBC 5 live sports extra.

Image source, PA

This is the semi-finals.

Great Britain are just two matches away from defending the historic Davis Cup crown that they lifted in Ghent last autumn.

After opting out of the quarter-final away in Serbia, world number two Andy Murray is back in the British team.

This is how the opening day rolls:

Andy Murray v Juan Martin del Potro

Kyle Edmund v Guido Pella

Followed by a spot of doubles on Saturday - in which Andy Murray is to team up with brother Jamie - and the reverse singles on Sunday.

Best of five, first to three, you know the drill.

Image source, Reuters

If it feels that we have been writing Juan Martin del Potro's wrist injury woes and comeback hopes for years, it is because we have.

Here is one from 2011. With a picture of the Argentine rocking some surfer locks.

This time though, you can believe the hype.

After nearly 12 months out and another bout of wrist surgery, he returned to action at Delray Beach in February as the world number 1042.

Since then he has beaten Novak Djokovic, Stan Wawrinka, Rafael Nadal, David Ferrer, Dominic Thiem, Giles Simon and Grigor Dimitrov.

As comebacks go, this is Elvis 68', rather than Stone Roses 16'.

Don't wonder about what might have been for a man who won the 2009 US Open at the age of 20, fear what he might do to Great Britain's Davis Cup defence in the days to come.

Image source, Getty Images

When Andy Murray locked racquets with Juan Martin del Potro in the gold medal match at Rio 2016, we were given a glimpse of what might have been. 

And what might still be.