Andy Murray is making the extraordinary his everyday.

A superb scampering forehand, hit from level with his kneecaps, swoops and dives across court to take the first point of the set.

Juan Martin del Potro survives though, hanging onto his popping serve like Kate Winslet clutching a bit of Atlantic driftwood.

James Stevenson: Never write off Andy.

A long old wait for the start of the fourth set as both players disappear somewhere behind the scenes for a comfort break.

Even umpire Pascal Maria seems keen for a leg-stretch, jumping out of the crow's nest to have word with the protagonists.

Here we go...

Great Britain's doubles player Dom Inglot: "Andy keeps on surprising us and I don't know why because he does it every single time.

"Andy needs to get fired up to play his best. He has worked out to rush the Del Potro backhand and that is the weak area of the court. I think Andy realises what he has to do.

"I think Andy will win this set. I think he will get it going and the biggest thing is that he starts this set well."

This should have been a simple smash for Murray, but he completely mishits the shot and still wins the point. Hit play below to see Murray's little grin as even he cannot believe how badly he hit the smash. 

That is the clincher. Andy Murray serves hard, wide and in. Juan Martin del Potro lunges , but can only dribble the return back into the net.

Two sets to one and the wind in the sails of the fair ship Murray.

Andy Murray into the net. Del Potro can only fend, a thumping overhead into the crowd via the court floor and it is set point Great Britain.

Andy Murray twangs a forehand into the net as he goes down the line. 5-5 and on serve.

A framed forehand into the heavens and Andy Murray's mini-break is dust. 4-4 and tension cranking north in the Emirates Arena.

Murray settles some nerves with a commanding point for 5-4.

Juan Martin del Potro with a string-stretchng forehand down the line shuffles up to within a point. 4-3.

Where have you been you little blighter? Andy Murray's first serve has come to the party. 4-1 to Great Britain and a mini-break to the good.

Murray snaps a return into the net, 4-2 and a towel down.

Image source, PA

Andy Murray drifts a little long to concede the point. That is a bit of waste after getting into the point. 2-1

Ace number 19 off Murray's first serve. 3-1

Andy Murray holds serve in the opening point. 1-0.

And then clambers into a return, smearing a second-serve winner past Del Potro for 2-0 and a mini-break.

Del Potro slips off the hook and we are into a tie-break.

Image source, EPA

Andy Murray milks the mistake from Juan Martin del Potro with a block return that asks the Argentine to make the pace in the rally.

Thirty-all.

The rallies are getting shorter.

Del Potro to 40-30 with a blockbuster of a serve, but Murray is into a rally on the next.

He invites Del Potro into the net for a game of sharp volleys. And comes out on top,

Deuce.

John Lloyd
Former GB Davis Cup captain on BBC Two

It is a measure of how great a player Murray is now that you expect him to do what he just did.

To hit that lob, set point down, you just expect him to make it.

It is just remarkable. 

Andy Murray charging like a rhino.

Forty-love via a steaming pile of ace pie.

The Glasgow crowd greet it with synchronised slap-downs in the stands.

Another crackerjack tee-off - rammed into the ribs of Del Potro- seals the deal.

Image source, EPA

Tom Gumbleton: @andy_murray WHAT. A . LOB......

Karen Turner: The audacity of those shots from Murray...incredible!!!

John Lloyd
Former GB Davis Cup captain on BBC Two

Andy Murray has to almost calm down a little bit after those last few points.

Del Potro, what must he be thinking?