Andrew Castle
BBC Sport tennis commentator

Djokovic has won seven tournaments this year - he had a phenomenal start to 2016, but he's tailed off a little since.

Goffin is not finding his range consistently enough to really trouble Djokovic. Especially at big points. A forehand goes long, allowing Djokovic to wrap up the hold.

Djokovic races into a 40-0 lead, but again leaves the side door slightly ajar. Goffin leathers a wonderful winner, then Djokovic spanks a forehand wide of the tramline. That's 40-30. 

Goffin draws him into another baseline joust and Djoko goes wide again. Same place as the previous point. Deuce...

A David Goffin superfan is picked out by the cameraman. He's holding up his prized possession - a framed photograph of him and the Belgian. Is that quite sweet or a bit weird? I'm not sure. Let's hope David has a burly security guard with him when he leaves later just in case.

Anyway, the chair of the Goffin fan club has something to cheer. His man holds serve at the start of the second set.

Image source, Reuters

Andrew Castle
BBC Sport tennis commentator

Goffin is playing OK, but there's no real problems here for Novak it would seem.

Easy peasy. Djokovic rattles through what he hopes to be the final game of the opener.

Two set points. The first goes begging with a double fault. No mistake with the second. Goffin goes long and heads back to his seat with some thinking to do.

Piers Newbery
BBC Sport in London

He's not the first and he won't be the last, so let's not blow this out of proportion, but that was a lengthy old rant from Djokovic to umpire Fergus Murphy at the changeover, and the tournament supervisor Tom Barnes.

It didn't seem an especially obvious violation of the time rule, so you can understand Djokovic's frustration, but he would do well just to brush it off and move on at 4-1 up.

Image source, Reuters

Don't make him angry. Novak Djokovic does his best Incredible Hulk impression - without turning green and popping open his navy blue shirt. The world number two channels his anger positively, racking up another pair of break points.

Can he convert? Yes. He's motoring along down the ATP highway and about to get off at the Set 1 junction.

Image source, Reuters

Andrew Castle
BBC Sport tennis commentator

Fergus shouldn't be getting involved in things like that. He hasn't done anything wrong really... but just leave it. He knew Novak was highly strung. He's quite prickly at the moment.

Tim Henman
Former British number one on BBC Two

Fergus Murphy has gone to the letter of the law, rather than giving him a warning. Djokovic should just get on with it. He's 4-1 up and hasn't actually lost anything yet. I do, however, think it was harsh on Novak.

Djokovic has been a little prickly over the last few days, clipping a ball at coach Boris Becker then snapping at a journalist when asked about it.

So that time violation is not going to please him. The Serb sees off Goffin after deuce, then tears into referee Fergus Murphy for the warning. Players have 20 seconds between serves at the ATP Finals, Djoko is clocking in about 23 seconds.

Andrew Castle
BBC Sport tennis commentator

That was beautifully done by Goffin and was quietly acknowledged by Djokovic.

Let's not forget this is Goffin's first gander at the O2 court. But that doesn't affect his hands. The Belgian produces a sweet lob that sails over Djokovic's head and dusts the baseline for 30-30.

Djokovic composes himself then receives a time violation. Djokovic looks perplexed. Like a bloke who has just received a speeding ticket when he was doing 41mph in a 40mph zone...

Tim Henman
Former British number one on BBC Two

This court has felt warmer than it has been in previous years. It means the ball is more lively and travels through faster.

For the first time we see a baseline battle. Point after point the two men play a tennis tug o'war. To me, to you. Djokovic and Goffin are doing their best Chuckle Brothers impression. In deuce number four, Goffin misses a sitter and then double faults again. Pressure. Djoko  draws first blood.

Image source, Rex Features

Andrew Castle
BBC Sport tennis commentator

There's something missing with Novak and his shot selection. He's questioning himself when there was once no question at all.

Double faultatitis is spreading. Goffin suffers a bout of it, letting Djokovic back into the game at 15-30. He brushes that off to level, then crashes down a 126mph ace - the first of the match - to move within a point of another hold.

That disappears down the drink quickly. Deuce...

Image source, Reuters

David Goffin, speaking to BBC Sport before the match: "I'm really happy to be playing. It's the best way to finish the season, to play Novak here in this competition. He is determined to reach number one again."

An easy hold here for Djokovic, surely? He finds his rhythm on his second serve, Goffin batting three of them into touch as Novak races into a 40-0 lead. 

But wait! Djoko punches a forehand well wide of the paint, then knocks one long. 40-30 - a sniff for Goffin?  Yes. A crackerjack of a forehand from the baseline leaves Djoko flummoxed and only able to applaud his opponent's winner.

Deuce sees Djokovic take control again, seeing out the hold.