Tomas Berdych's forehand is starting to fire.

A couple of crashing strokes off his favoured wing take him to 30-0.

But he is also showing the touch of a miniature portrait artist.

A deft backhand pick-up half-volley is too good for Djokovic, tapping down twice to close the game.

This is a lot tighter that many had predicted pre-match.

Image source, AP

Tomas Berdych darts to the net at 15-15. Djokovic pumps down the line onto his backhand and the Czech plants away a winner.

15-30 and a chest-swelling point to make the world number six dream impossible dreams.

That morale boost is what Berdych will have to take from the game though. Djokovic shuts the rest of it down to edge back ahead.

Leon Smith
Great Britain Davis Cup captain

He really is a strong, strong athlete. He generates good speed on his serve. He's an exceptional player and what makes him just off the top five is maybe a little bit of movement.

Image source, AP

Tomas Berdych clambers back from six feet under to make it  to deuce.

Djokovic trains fire on the Berdych backhand and this time it stands firm. Advantage to the Berd-man. And then a popping ace to complete the escape!

Could that hold be the making of him in this match?

Djokovic is asking questions of Tomas Berdych. And they are not about his Christmas plans.

The big Czech's movement is found short when inquiries are made out wide by the world number one.

Love-30.

Berdych knows he has to play lights-out knock-out tennis to get the straight-sets win he needs.

But he has over-cooked a backhand long. Love-40 and three break points Djokovic.

Tomas Berdych has attracted some sympathy support and the match is not three games old.

The Czech's double-handed punch down the line for a winner and 15-30 is given hearty cheers by a crowd who are fearful that their evening's entertainment is going to be over sooner than they wished.

This is more like it as the topdog is taken to deuce.

Djokovic is a little hurried on his backhand wing and plonks into the net. Break point Berdych.

And Djokovic nets!

Maybe some of that pity was a little premature...

Image source, EPA

Tomas Berdych is staring down the opposite end and seeing an ogre.

His big serve is cowed by the prospect of Djokovic's whip-smart return and he slides to 0-40 in dispiriting fashion.

Three break points. Djokovic goes for the grind on the final rally, pummeling back strong and deep, but never too wide, as he challenges Berdych to chance his arm.

Berdych coughs up the error long and has won only one of eight points so far in the match.

Novak Djokovic looks tight and tidy off the tee in the opening game.

He peppers the corners of the service box and loses only one point on his way back to his chair for a slug of something that looks like strawberry milkshake but is doubtlessly much, much healthier.

Novak Djokovic to serve.

Tomas Berdych, decked out in brown and beige, to receive.

Image source, Getty Images

The glimmer of hope for Tomas Berdych?

Well, Djokovic and his last meeting was only two weeks ago at the Paris Masters event, on a court similar to the one at the O2.

It was a straight-sets win for Djokovic, but both of those sets went to tie-breaks.

Could they have crumbled the Czech's way?

Image source, Getty Images

The head-to-head record between Novak Djokovic and Tomas Berdych is so lop-sided that it broke the scales.

Djokovic has won 20 of their previous 22 meetings, including all 17 on hard courts.He has won their last seven matches.

As their credentials are read out by the O2 emcee, the difference is marked. 

Twenty-six ATP 1000 titles for Djokovic, along with 10 Grand Slam titles. Berdych has just one Masters 1000 title.

Image source, Getty Images

This match is slightly later out on court than advertised (by me anyway) after Jamie Murray and Australian double partner John Peers were taken to a match tie-break in an epic final round-robin encounter against the top-seeded Bryan brothers.

Five match points went begging for the Anglo-Aussie pair - one a clear forehand chance for Peers - before their succumbed 16-14 in the shoot-out.

It was Murray and Peers final outing as a pairing. They go their separate ways at the end of this season and Murray will partner up with Brazil's Bruno Soares.

Image source, Reuters

Novak Djokovic has been a man apart from the rest this year, but a straight-sets defeat by Tomas Berdych tonight would deprive the O2 semis of the best player in the world.

The man himself has been warming up in east London with a giant space hopper.

The players are due on court shortly.

Image source, Getty Images

The Serb has won 79 out of 85 matches overall this season and was an on-fire Stan Wawrinka away from a calendar Grand Slam.

He has been flying solo in first class, confining the likes of Andy Murray and Roger Federer to the back with the hoi polloi.

However he was brought to earth with a bump by Federer on Tuesday as the Swiss legend prevailed 7-5 6-2 in their round-robin meeting.

Image source, EPA

Between 23 August and 17 November:

Mo Farah completed a second successive world championship distance double.

Brendan Rodgers lost his job as Liverpool manager.

New Zealand won the Rugby World Cup

And Novak Djokovic won all 23 of the tennis matches he played.

Image source, EPA

The evening match at the O2 Arena is Tomas Berdych against world number one Novak Djokovic.

Djokovic - on the back of one of the stellar seasons in tennis history - would fail to make the last four of the World Tour Finals if Berdych beats him in two.

It couldn't happen. Could it?

We will be back at about 19:45 GMT to find out....

GB captain Leon Smith on his possible number two pick: "Kyle Edmund, Dan Evans and James Ward have all won Challenger events recently. It is going to be a very difficult decision but it will be for the betterment of the team.

"I will let the players know as soon as possible.

I will rally the possibilities around in my head for a while, consider the surface, the match-ups and the experience."

Leon Smith has come up to chat with Sue Barker in the BBC studio for a little look-forward to the Davis Cup final next weekend.

"We are going to see an incredible quality of fight and passion from Andy come the final," he says.

"He keeps surprising me, his ability to produce the type of tennis he does under stress, fatigue and pain. He just gives everything every time he pulls on the shirt.

"He is the superstar, but his support for the team is phenomenal."