Andrew Castle
BBC Sport tennis commentator

A good start from Goffin, he got the job done there. The top Belgian has improved his year-end ranking for a third season in a row. For a long time, the Belgian men - while good - were outshone by the likes of Justine Henin and Kim Clijsters.

Job done. Goffin, ranked 11th in the world, holds as Djokovic goes long with a forehand. A big sigh from the Serb as waits to grab a couple of balls for his service game. Come on Novak, life can't be that bad.

Image source, Reuters

Andrew Castle
BBC Sport tennis commentator

Goffin isn't going to blow too many people off the court, so he has to control the ball and that will help him to control his opponent. He's showing some nice depth to his returns at the moment.

Image source, Reuters

Let's see what the Goffin serve has to offer. Not much initially, Djokovic swatting away a winner to rattle off a fifth straight point.

Goffin, with those piercing blue eyes, stares back across the net. The sort of look that means business. He steams 40-15 ahead as he pins Djokovic back, but then the Serb wrestles back control. Deuce...

Wow. A murmur rumbles around the O2 as Novak makes a shocker of a start. TWO doubles faults gift a 30-0 lead to Goffin. Easy this World Tour Finals isn't it?

Ah, not so. Two overcooked forehands from the Belgian wipe out that advantage, Djoko sticking his foot down on the pedal to hold.

Joel Newnham: The crowd will want Goffin to win. That will help Murray.

Image source, Reuters

Let's get ready to rumble. Djokovic has the honour...

Novak Djokovic, speaking to the media before this match: "I've never felt unbeatable, and I never will. I don't think it's right to ever say you're unbeatable. Few athletes retire without losing. But I don't feel vulnerable..."

Image source, Reuters

Tim Henman
Former British number one on BBC Two

Every point is vital. Andy and Novak have separated themselves from the rest this year. Every match is worth 200 points and Novak is not used to going into matches ranked as number two in the world. He wants to end the season on top.

I wonder which Novak Djokovic will turn up today. The one who looked like a human-beating robot or the one who looks, well, human. 

The Serb is attempting to win a fifth straight World Tour Finals - a result which would ensure he reclaims the world number one spot from Andy Murray. 

Piers Newbery
BBC Sport in London

'Dead rubber', did I hear you say? Not this week.

The battle for the year-end number one ranking means every group match is significant for Djokovic, even though he has already qualified for the semis. He needs to better Murray's results at the O2 and the pair both currently have 2-0 records.

There are 200 points on offer for each group match so a win here would effectively sneak Djokovic ahead, before a presumably exhausted Murray takes on Stan Wawrinka on Friday afternoon.

The match referee flings up a pearler of a coin as the two players contest the toss. It is the sort of bit of silver that a coin collector would keep under lock and key. Djoko to kick off.

Andrew Castle
BBC Sport tennis commentator

This should be a good match to watch. It's a tough ask for Goffin to just step in and mix it with the likes of Djokovic, but he looks to have prepared in the right way.

David Goffin is the first fella to walk out into the O2. Looks like a nightclub. Dimmed light punctured by some strobes, a bit of EDM pumping out of the sound system.

Novak Djokovic dances in behind him. OK, he doesn't. He walks out calmly - a picture of concentration.

Image source, Reuters

Lights, camera, action. Sue Barker is rolling. That means you can tune in to BBC Two (or watch right here on this page). Tim Henman and Andrew Castle are her sidekicks.

Piers Newbery
BBC Sport in London

There are not many people who have been at the O2 this week who have not bumped into David Goffin doing some very strenuous stretching. The Belgian has seemed to be lunging around every corner, between vigorous practice sessions with any other players in need of a hit. He is up for it.

The role of 'alternate' is a strange one, with tournament veteran Tomas Berdych preferring to head to the Maldives with his wife rather than take up the £80,000 on offer for a place on the sidelines this year.

Goffin, on the other hand, is a man on the up and keen to just spend a week in the elite club. His unexpected chance at competitive match action could yield another £144,000 if he manages to beat Djokovic.

Laura Cooney: I feel a bit sorry for David Goffin having to play a dead rubber. Does he at least get ranking points if he wins?

We believe he does, Laura. And don't feel too sorry for him...

I wonder what David Goffin has been doing all week. As well as crossing his fingers that someone would get injured, of course. Stood outside Buckingham Palace taking pictures? Been on the London Eye? Checking out record shops in Shoreditch? Who knows.

Strange old week for the Belgian.

Image source, EPA

So Gael Monfils will be resting in his hotel room this afternoon instead of pounding the O2's blue acrylic.

The Frenchman had to pull out of the tournament after struggling with a rib injury sustained in Stockholm in October.

"I tried to make it, but I couldn't," said Monfils, who has lost to Dominic Thiem and Milos Raonic at the O2.

Just as well. Monfils has a stinking 0-13 record against Djoko. Not that we're suggesting that played any part in his thinking, if his lawyers are reading.