The match is scheduled to start at 18:00 GMT.
Djokovic was first to move through to today's showdown. Although he threw in some unexpected wobbles during round-robin play – including during a 7-5 6-2 loss to Federer – the Serb was never in serious doubt to miss out on a place in the final. His first result was a 6-1 6-1 crushing of Kei Nishikori, and his final group stage win a 6-3 7-5 dismissal of Tomas Berdych.
There was a lot of excitement surrounding his semi-final clash with Rafael Nadal. The 14-time Grand Slam champion, who has struggled for confidence and form all year, went lossless to top the opposing round-robin group - and with a 23-22 head-to-head lead on the Serb, many hoped for a traditional epic duel from the pair.
There was concern that Nadal – rested a day less than Djokovic – would be too fatigued for the fight after a 2 hour 40 minute fight with David Ferrer the previous day. However, the match was ultimately not about what Nadal couldn't do, but what Djokovic could. The world no. 1 was clinical off forehand and backhand, stepping up to the ball and disabling the renewed aggression that the Spaniard had borne in London thus far. He never faced a break point during 6-3 6-3 win – sending a clear, warning threat to his final opponent.
Federer topped his group with a perfect 3-0 record, the Swiss securing a 6-4 6-2 win over Tomas Berdych before his victory over Djokovic, and a tougher 6-4 4-6 7-5 victory over Kei Nishikori afterwards.
The largely iffy standard he brought to that encounter with Nishikori initially showed up for his clash with Stan Wawrinka. The last time the two had contested a match at the O2 Arena, Wawrinka surrendered four match points in a loss to Federer at this stage last year. Perhaps the 34-year-old was tight – knowing that his compatriot could potentially pull anything out of the bag, and that there was suddenly no safety net spread beneath a loss in this penultimate stage. Whatever the cause, he was clearly ruffled by his errors as he went down and early break at 4-2, first set.
But from there, Federer upped his game and never looked back, breaking to get back on serve and then going all out at 5-6 to break for the set.
As he often does, Wawrinka – a perfect combination of epic and erratic – erred to the wrong side of himself for the rest of the match. Despite moments of resistance, he could only watch as the no. 3 seed held to love for a 7-5 6-3 victory.
Last year, an injured Roger Federer had to withdraw prior to taking on Djokovic. But no such woe looks about to strike him again this year.
Federer has already beaten Djokovic three times this year - equal to what the rest of the tour have managed between them. He leads his overall head-to-head record with Novak Djokovic 22-21. The Swiss won their most recent clash, of course, in the round-robin stage this week - but Djokovic leads their overall 2015 head-to-head 4-3.
On indoor hard-courts, Djokovic leads by slim margins once more: 4-3. But here at the O2 Arena the pair are drawn at 2-2. And in what could be the most interesting statistic of all, Roger Federer leads in all-time best-of-three set
meetings by 16 triumphs to 13.
Winning in the group stage might not have been the best thing for Roger Federer in the long run. The likelihood is that both would have qualified for the semi-finals anyway, and the Serb now knows what he has to correct against his forthcoming opponent. What is more, while Djokovic has been going from erratic to clean, Federer has shown small signs of descending in the opposite direction. Surely, Novak Djokovic will not forgive a slow start like that of the third seed's against Wawrinka.
But Federer is showing the world a legendary longevity of a true champion. He has looked highly comfortable at the O2 Arena so far this year. Undoubtedly, the last ATP final of the season will be a riveting clash between 2015's brightest stars.