Settle in, because we could be going the distance. Nishikori was looking so shaky, but somehow found a break. Murray was pushing all the buttons in the fourth set, but now finds himself staring at a decider. It's flat in Birmingham too.

Now then. Huge danger for Murray. From nowhere, Nishikori has found two break points. The crowd bangs the drum, right behind the Scot. What's he got?

John Lloyd
Former Davis Cup finalist on BBC Two

Image source, PA

"The standard of tennis has dropped but this is now a battle of wills, and when it comes down to it, I think Murray wins on that regard."

Nishikori comes through, gobbling up a forehand into open court. It's a real slugfest, two men scrambling through the quarry on their hands and knees. Not pretty, but compelling.

Colin R. Parsons: I feel tired just watching this match.

Emma_Jayne: I'm meant to be packing up the house but can't stop watching Murray's match. Oops.

Image source, Reuters

When he needs one, Nishikori finally gets a first serve into the right postcode. He's puts the overhead away, elongating this game... 

Netted forehand from Nishikori! Break point. Virtual match point?

Andrew Castle
BBC Sport tennis commentator

"It is not hard to understand why the best players do not play Davis Cup every year. It is a lot of weeks, a lot of energy, each year if you get a run going."

You just feel like Murray is getting back into it. His holds have been easier, Nishikori is finding it tougher. Even the Scot's facial expression has changed. From passive to aggressive. 0-30, Nishikori begging for a first serve. Murray with too much on a forehand, looking for a winner. Back to 30-30. Then the angry Murray goes into the net, but, from nowhere pulls out a belting backhand winner.

Onwards...

Image source, EPA

GB and Japan are fighting for a quarter-final place, where they would play either Serbia or Kazakhstan. The smart money was on the hosts to prevail in Belgrade, with the seemingly invincible Novak Djokoic leading the way, but they trail 2-1 and the world number one is having all sorts of trouble drawing them level. He has just forced a fifth set against Mikhail Kukushkin - with four hours and 17 minutes already on the clock.

For your viewing pleasure, the end of the third set...

Lovely from Murray, the best tennis he has produced for some time. Nishikori doesn't get a sniff in what is a hold to love.

Nishikori gets through, Murray going wide with a backhand. Noise non-existent in the second city. It's too tight to speak.

Andrew Castle
BBC Sport tennis commentator

Image source, Reuters

"You can just feel the fatigue in the air from these competitors. This is a grueling game."

Murray's legs just give up on him, the break point goes into the net. More chuntering - such anger at the world - then Murray stops himself from smashing his racquet when he puts a forehand wide. Nishikori, though, is having his own problems when it comes to keeping the ball in court. Fatigue on both sides of the net, tension sky high.

John Lloyd
Former Davis Cup finalist on BBC One

"There are some shaky points now from the Japanese number one."

Image source, PA

Is this the moment? Wide backhand from the Japanese. Huge break point coming up...

John Lloyd
Former Davis Cup finalist on BBC One

"Andy is fuming. The umpire is going to get an ear-full this next change of ends."

Murray is running, covering more ground that at the end of the previous set, but it's not quite enough. He lets out another trademark scream - who are those directed at? - and his mood isn't improved when a late challenge goes the way of Nishikori. Still, a horrible fault from the Japanese gets Murray back to 40-40.

John Lloyd
Former Davis Cup finalist on BBC One

Image source, Reuters

"Murray is so good, you just feel somehow he will find a way to win this match, even though he looks tired at times."