David Law
Radio 5 live sports extra commentator

I find Thiem really interesting to watch - when he hits his groove, I think he's as spectacular a ball striker as anybody.

Let's see what Dominic Thiem has got in his locker then. A mis-hit when Raonic returns his opening gambit. After that, it is impressive stuff. Thiem finds his range thundering down three more first serves that Raonic cannot scoop back over the net.

Leon Smith
Great Britain Davis Cup captain on Radio 5 live sports extra

It's important that Thiem serves well tonight because he won't get many opportunities to break Raonic's serve.

Why has Thiem opted to receive first? Probably to try and catch Raonic's big serve cold. No, the Canadian is cooking already. He thunders down an ace - surely the first of many - on his way to hold to love.

Back to business inside the arena... It's show time. The near-capacity 18,000 fans settle down in their seats. Presumably with a large bucket of popcorn. Sweet rather than salted hopefully. Raonic to kick off...

Piers Newbery
BBC Sport in London

While the singles players get ready to take centre stage, the victorious doubles team have been through the press room. Jamie Murray and Bruno Soares know that they will end the year as the number one pairing if Pierre-Hugues Herbert and Nicolas Mahut lose on Friday.

But wouldn't they rather win it on court themselves?

Jamie Murray: "Don't really care.

Bruno Soares: "No, I care. Finish for us tomorrow. It's easier.

Jamie Murray: "That's true."

Image source, Getty Images

Jamie Murray and Bruno Soares are into the last four of the ATP World Tour Finals and on course to end 2016 as the world number one pairing. More on that here.

Time for the coin toss. Not your average 50p is the flipper of choice. More like one of those collectables that you used to get from Esso. Dominic Thiem correctly calls, opting to let the big-serving Milos Raonic thump down the ball first.

Leon Smith
Great Britain Davis Cup captain on Radio 5 live sports extra

The arena is unbelievable - the atmosphere, the way everyone is treated on and off the court. It should be special, being the end of season tournament, and it certainly is.

Raonic is back out of the khazi, sorry, changing room. He marches out of the tunnel with a stature and facial expression that Ivan Drago would be proud of. Dominic Thiem looks a little more relaxed. 

Milos Raonic is pacing up and down a grey-walled corridor in the bowels of the O2. Like a man who is just about to find out whether that job interview was successful or not. Then he nips back into his changing room. Maybe he needs a quick comfort break.

Milos Raonic, speaking to Sky Sports: "My body feels great. I feel I have what is required to win this match. I need to serve well and dictate."

Dominic Thiem, talking to Sky Sports: "I feel good tonight. After two three-setters it is not easy but I'm ready for it.

"He is one of the best servers in the game so I have to return many serves. Then I have to do well on my service game but it isn't going to be easy."

Apart from the manner in which he dismantled Goffin, the other talking point from Djokovic's win was a row with match referee Fergus Murphy.

The Serb was given a time violation. To say he did not take kindly to it is being generous.

Image source, AP

One man is already through to the semi-finals. And that's the new world number two.

Novak Djokovic does not plan to be the second best player on the plant for very long, and he is breathing down Andy Murray's neck.

The Serb, whose name is already scratched into the last-four draw, completed the group stage in fine style by thrashing David Goffin earlier today.

Remember, Djokovic needs to better Murray's results in London to overtake the Briton in the rankings.

Dominic Thiem is doing a version of the 'Can-Can' in the O2 corridor. Presumably to stretch those hammies. Now he is doing the Time Warp...

When your Dad picks you up from school, takes you to the tennis, bags the best seats in the house, and is the most famous person (probably!) inside the venue. Romeo Beckham has got a cool dad.

Image source, PA

Won one, lost one. Both Raonic and Thiem beat Gael Monfils but lost to Novak Djokovic. So the winner of this match will finish second in Group Ivan Lendl behind Djoko.

The O2 Arena is filling up quite nicely, including a few familiar faces...

Image source, Getty Images

Now, I've got no idea whether two of tennis's hip young gunslingers are Abba fans. I'd guess not. 

But they could be forgiven for having the chorus of 'The Winner Takes It All' in their head.

Because the winner does take it all tonight. One place is up for grabs in the ATP World Tour Finals semi-finals.

Milos Raonic? Or Dominic Thiem? Whoever wins tonight's showdown.

Image source, Getty Images

Whoever is charged with spinning the tunes on the O2 Arena's decks has a clear brief. 

Something fun. Something noisy. Something the kids like. Something like D'n'B or EDM. Certainly nothing older than the eight blokes who we're all here to see.

But, tonight, that person might be tempted to dust off an Abba classic.

"The winner takes it all, the loser has to fall...."