Great Britain have a mountain to climb if they are to keep hold of the Davis Cup.

It is likely to require Kyle Edmund to beat Juan Martin del Potro.

We will be back tomorrow for the doubles match that gets under way at 14:00 BST.

Guido Pella speaking on court: "I am very happy. This is a team and I am happy to give the team a second point after Juan Martin's amazing match. I was fighting every point no matter what, and at the end of the third set I was playing really well. I think that was key."

Kyle Edmund is raging hard against the dying of the light, but his forehand is slowly disintegrating.

A bosh long off that wing brings up 30-30.

That is a 47th unforced error.

Pella forces deuce and then a break point as he comes out on top in a game of cat and mouse at the net.

Edmund bunts a backhand long and that is the double break.

The disc jockey misreads the majority mood and lobs on a bit of the Outcasts' Hey Ya.

Image source, Reuters

Kyle Edmund with a glimmer at 30-30.

But Guido Pella thumps down a T-splitter of a service, slashing away a winner off Edmund's pattercoake return.

A kicker out wide from the Argentine and that is the visitors another game closer to home.

Kyle Edmund batters though a service game to love.

Great Britain captain Leon Smith is immediately cosying up to him on the courtside bench offering up some pearls for the forthcoming return game.

Guido Pella only needs two three more successful successive service games to wrap up this rubber. 

Image source, Getty Images

Guido Pella's touch at the net is silken.

The Argentine kills a stretching drop-volley stone dead for 40-0 and is waved on through to the game as Kyle Edmund frames a forehand towards the roof.

It is difficult to see how Kyle Edmund is going to recover this break.

Kyle Edmund is on the ropes, swaying like a sailor in the rigging, but he had dodged the knockout blow.

He holds serve and keeps his cards on the table in the decider.

A break there would have been very nearly curtains.

Image source, Reuters

Kyle Edmund has saved another two break points.

He is playing the big ones well so far. He has successfully defended 12 of the 17 break points that he has faced across the whole match.

Guido Pella is coming on strong.

A double-fisted punch down the line helps him to 0-30, before a ripper across court off the same wing brings up three break points.

Andy Murray has a 1000-yard stare on the sideline.

Kyle Edmund is blowing on the embers. He comes to the net to punch away a backhand volley for 30-40 and then picks off an advancing Pella to take it back to deuce.

Image source, PA

It is difficult to work out exactly how the momentum has changed.

Guido Pella is suddenly finding angles that he just wasn't hitting in the first set and a half.

He races into a 40-0 lead and some supreme chasing out wide forces Kyle Edmund into a front-court half-volley pick-up that he has not got the touch to make. 

Guido Pella sets up two break points with a fluttering butterfly of a drop shot that settles out of Kyle Edmund's reach for 15-40.

A lovely drop-volley seals the deal.

Kyle Edmund, who slid to defeat from two sets up on David Goffin in the Davis Cup final last year, is going to have to try and jumpstart something into life to turn the tide.

Image source, AP

Matt Henry has headed for the hills for the evening. Mike Henson back at the control as we head into the wilds of the fourth set.

Guido Pella with the momentum, Kyle Edmund with the majority of the home support,

Great Britain's Davis Cup defence on a knife-edge.

Here we go.

There are some worried faces in the British crowd.

Pella looks so solid and there are more and more errors coming from the Edmund racquet.

The Briton won both his matches in the quarter-final against Serbia though don't forget. Keep the faith ladies and gents. 

Image source, Reuters

Andy Murray has finished his post-match duties and is back courtside to support his 21-year-old teammate.

He hasn't brought much luck with him though as Pella breaks serve after the 38th unforced error from Edmund.

He led 3-2 with a break in this set but now Pella has won three games in a row and will serve for it.

Jamie Baker
Former GB Davis Cup player on the BBC Red Button

Looking at his body language and demeanour, it looks like Guido Pella is growing into this match. Kyle Edmund, by contrast, started well, but may be tightening up a bit.

Image source, Reuters

Without meaning to repeat ourselves, that Edmund forehand really is an impressive shot.

Two more winners in this game take us to deuce but Pella hits back with one of his own at the perfect time.

A long pause as the players are distracted by a hum in the arena, "it's the air conditioning,' says the umpire.

Pella deals with it and he's ahead again.

Jamie Baker
Former GB Davis Cup player on the BBC Red Button

"My one concern with how this is shaping up for Kyle Edmund is that the greater number of balls that Guido Pella is getting back is luring Edmund into trying tt hit harder and then his error rate creeps up.

"He needs to find different ways to win points."

Image source, AP

What is the saying?

A break is not a break until you back it up the next game?

A couple of errors from Edmund and it is 0-40. 

No, Kyle. His second double fault. The Argentinian breaks straight back.