World number one Rafael Nadal, who had overcome Roger Federer earlier in the day, awaited the winner.
Read how Djokovic booked his 39th meeting with Nadal below with Sports Mole's blow-by-blow text updates.
7.32pmThank you for joining Sports Mole's live coverage of what promises to be an exciting clash between two in-form men in North Greenwich.
7.35pmNovak Djokovic and Stanislas Wawrinka are due on court at around 8pm. Their match will directly follow tonight's doubles semi, in which the Bryan brothers are taking on Alexander Peya and Bruno Soares. That match is currently in a Champions Tie Break.
7.39pmDespite being replaced by Nadal as world number one earlier this year, Djokovic is the bookmakers' favourite to win the ATP World Tour Finals. The Serb has won all three of his matches at the O2 Arena this week, triumphing in three-sets against Roger Federer, Juan Martin del Potro and Richard Gasquet.
7.43pmWawrinka's place in the last four was only confirmed yesterday when Nadal beat Tomas Berdych 6-4 1-6 6-3. However, not many people would argue that the world number eight is lucky to be in semis. His only defeat this week was a narrow 7-6 7-6 loss to King Rafa on Wednesday. Wawrinka finished second in Group A, after registering victories over Berdych and David Ferrer.
7.47pmGAME SET AND MATCH! The Bryan brothers have beaten Peya and Soares 4-6 6-4 10-8. The top seeds will face Spanish duo David Marrero and Fernando Verdasco in the doubles final tomorrow.
7.50pmRight then, let's refocus on tonight's main event. Djokovic has won 13 of his 15 previous meetings with Wawrinka. Encouragingly for the Swiss, though, he has beaten Novak indoors (6-3 6-3 in Wien in 2006).
7.55pmWawrinka has just been speaking to Sky Sports in the tunnel. He said: "My level has been really good this week. I'm really happy to have beaten Ferrer and Berdych already, as well as a good match against Rafa. And I'm really happy to have another match here against one of the best players in the world. It's going to be tough match but I'm looking forward to it."
7.59pmNovak, who is about to take part in his 80th match of 2013, says: "It's been a long year, but a successful one, especially in the last part. I just want to continue that form. Stan has big power in his legs, a great one-handed backhand and a big serve. He is the complete player."
8.04pmPREDICTION: Both men have played some fantastic tennis this week, but it is almost impossible for me not to favour Djokovic tonight. The Serb is looking for his 21st consecutive victory on the Tour. I think he will get it in two tight sets.
8.08pmThe toss goes Djokovic's way and the Serb will serve first.
Djokovic 1-0* WawrinkaDjokovic fails to find a first serve on each the opening two points, which both go the way of Wawrinka as Novak fires wide with his backhand, then his forehand. However, the second seed stays calm and wins the next four points to hold to 30 with solid high-percentage tennis, drawing four errors from his opponent following lengthly baseline exchanges.
Djokovic *1-1 WawrinkaImpressive stuff from Wawrinka, who is put under pressure as Djokovic forces deuce. The Swiss responds with his first ace, followed by an unreturnable serve to Novak's backhand.
Djokovic 1-2* WawrinkaWAWRINKA BREAKS! The first break point of the match presents itself to Wawrinka at 30-40. Djokovic earns a brief reprieve thanks to a huge first serve, but the Swiss immediately earns another with a beautiful crosscourt pass. There is no let off for Novak at the second time of asking as Wawrinka seals the game with his seventh winner of the night.
Djokovic *2-2 WawrinkaDJOKOVIC BREAKS BACK! Parity is restored straight away, as Wawrinka comes up with two loose forehand errors from 30-30.
Djokovic 3-2* WawrinkaNovak holds to 15. The Serb seems happy to prolong the points, while Wawrinka is keen to keep them as short as possible. So far tonight, the average length of a point on Djokovic's serve has been seven strokes, compared to just four when Wawrinka has been serving.
Djokovic *3-3 WawrinkaWawrinka was in desperate need of a comfortable service game. And he manages to achieve just that - holding to 15.
Djokovic 4-3* WawrinkaNovak has been on target with just 65% of his first serves in so far. Nevertheless, he holds to love in game seven.
Djokovic *5-3 WawrinkaDJOKOVIC BREAKS! The Serb has turned the set on its head. He fails to convert his first break point, which comes at 15-40, slicing into the net at the end of a 24-shot rally. However, an incredible display of defence sees him get the break on the next point. The world number two, who will now serve for the set, has not even hit a winner yet! Such a disciplined performance.
Djokovic 6-3 0-0* WawrinkaFIRST SET TO DJOKOVIC! Novak produces his first winner early in game nine, before Wawrinka bites back to force break point at 30-40. However, a fantastic response by the defending champion sees him win the next three points to seal the opening set, hitting a glorious forehand pass and an unstoppable ace in the process.
8.58pmIt was Wawrinka who played most of the big shots in that opening set, hitting eight winners to Djokovic's three. However, Novak has an incredible knack of just getting the ball back into court time after time. As a result, Wawrinka keeps being tempted to attempt risky and low-percentage plays.
Djokovic 6-3 *1-0 WawrinkaDJOKOVIC BREAKS! The Serb races out of the blocks at the beginning of set two, winning the opening three points to bring about three break points. Wawrinka saves the first two, but the seventh seed then fires wide.
Djokovic 6-3 2-0* WawrinkaDjokovic holds to love. He has now won 14 of the last 19 points.
Djokovic 6-3 *2-1 WawrinkaStan gets himself 30-15 ahead, but Djokovic soon forces break point by coaxing the Swiss into taking on two all-or-nothing backhands, which both fail to find the court. Another Wawrinka backhand is then called wide, only for Hawk-Eye to come to his rescue, giving him a second life, which he gratefully uses to earn a gritty hold.
Djokovic 6-3 3-1* WawrinkaIt took Djokovic 50 points to register his first winner. He now has six, as he holds to 15.
Djokovic 6-3 *3-2 WawrinkaDjokovic benefits from a dead net cord to move 15-30 ahead before going on to create break point at 30-40. Wawrinka's second backhand winner of the match saves the break point. Another then comes and goes before Stan clings on to keep his faint hopes alive.
Djokovic 6-3 4-2* WawrinkaDjokovic holds to love. His backhand has been simply flawless tonight, in terms of both length and width.
Djokovic 6-3 *4-3 WawrinkaAnother break looks to be on the cards at 15-30, but Wawrinka storms back, powering a 133mph ace past Djokovic before sealing a hold to 30 with another massive serve.
Djokovic 6-3 5-3* WawrinkaNovak holds to 15, moving him to within one game of a place in tomorrow's final.
Djokovic 6-3 6-3 WawrinkaGAME SET AND MATCH DJOKOVIC! The Serb breaks to 15 to seal a brilliant straight-sets victory after 85 minutes. Watch out Rafa, Novak's coming for you!
9.40pmThe tournament favourite has now won 21 consecutive matches. Monday's end-of-season finale will fittingly be world number one versus world number two.
9.43pmNovak, speaking to Sky Sports: "It was a very enjoyable match for me. The performance was definitely by far the best I have had in the tournament."
9.46pmAsked whether he is unbeatable right now, he replies: "I don't think that's the right word. Nobody's unbeatable. Being at the present moment and taking it one step at a time helps me keep my focus."
9.47pmThanks for joining Sports Mole this evening. I hope that you will be back tomorrow for the big one. Until then, good night.