Piers Newbery
BBC Sport in London

As ever when the top players meet, there is a blizzard of stats to battle through in the search of the key factor in what is about to unfold. 

What we do know is that Murray could do with making a fast start today - Djokovic’s record against Murray after winning the first set is a crushing 19-0. Bearing in mind the miles in his legs this week, a Murray comeback would be quite an achievement.

A mix of sublime and tough is an appropriate description of the Scot's passage to this stage.

He began with a relatively comfortable win over Marin Cilic before a three-set record-breaking 200-minute encounter against Kei Nishikori.

His final John McEnroe Group game was against Stan Wawrinka who he, well let's be blunt, demolished.

On to the semi-final. It was widely expected that Murray would ease past Milos Raonic, the player who had beaten six times this season, including wins at the Queen's Club and Wimbledon finals.

But it was anything but easy. The Canadian world number four won the first set and looked unbreakable before Murray summoned all the energy he could muster to pip his opponent 11-9 in the final set tie-break.

That contest lasted a tournament-record three hours and 38 minutes, beating the mark set on Wednesday.

What has Murray left in the tank?

This interview with "Supermac" was first published two days ago, but all very relevant. 

Piers Newbery
BBC Sport in London

Mats Wilander, former world number one: "The tough thing for Murray is he hasn’t beaten Novak in a big-time final for a number of years, but what an unbelievable match. No wind, no rain, no sun, three sets, it’s a shoot-out between the two best players in the world and they’re still fighting for number one. I’ll be watching."

Image source, Rex Features

Liverpool v Arsenal, 1989

Wales v England, 2013

Middlesex v Yorkshire, 2016

Trump v Clinton, 2016

Alien v Predator, 2004

The ultimate showdown. Two rivals going for the title of 'the best in their business'.

In a few minutes, Andy Murray will take to the O2's deep-blue court in an attempt to win the ATP Finals title which would see him hold on to his new world number one ranking.

The man who could deny him both honours is world number two Novak Djokovic - the player he dethroned earlier this month.

The best-of-three sets encounter begins shortly. Live BBC Two and BBC Radio 5 live coverage gets under way at 18:00 GMT.

We are under way now.