Novak Djokovic will hope to build upon his opening ATP Finals victory when he returns to the court against Alexander Zverev on Wednesday afternoon.
The world number one produced a clinical performance to defeat John Isner 6-4 6-3 and will look for more of the same against Germanys Zverev.
In the evening session, the two losers from the opening round of matches, Isner and Marin Cilic, will go head-to-head, hoping to keep their hopes of progressing in the tournament alive.
ATP Finals 2018 groups
Novak Djokovic v Alexander Zverev (not before 2pm)
Djokovic produced a returning masterclass against big-serving American Isner on Monday night to send a chilling warning to the rest of the ATP Finals field.
After a poor start to the year, Djokovic found his top form in Wimbledon and has not looked back since. He lifted his second Grand Slam title of the year at Flushing Meadows, before reclaiming the number one ranking from Rafael Nadal.
He is comfortably the best player in the world right now and can stamp his authority on group Gustavo Kuerten with a victory over Zverev.
Djokovic smashed Zverev 6-2 6-1 in Shanghai last month but the German does at least boast a victory over the Serbian legend, having beaten him in Rome in 2017.
Zverev will have to be at his best to trouble the great Djokovic and the early signs have not been promising. The 21-year-old was 4-1 down in the opening set of his opening match against Cilic and was fortunate to be allowed a reprieve.
He improved as the match went on but will need to raise his game even further if he hopes to spring an upset in London.
Prediction: Novak Djokovic in two
Marin Cilic v John Isner (not before 8pm)
Two players who suffered rather different defeats in their opening encounters. While Isner was simply outplayed by Djokovic, Cilic was in control of his match against Zverev before falling to pieces.
For a player of Cilics experience – he is a former US Open champion and Wimbledon and US Open finalist – to self-implode as he did was alarming.
The Croat giant has never performed at the ATP Finals, winning just one of his ten matches at the season-ending event.
And debutant Isner could take advantage after enjoying his best-ever season on the tour. After winning in Miami, Isner enjoyed fine runs at Wimbledon and the US Open.
His serve gets much attention, and rightly so, but Isners ground strokes and movement have improved beyond measure over the last 18 months.
Cilic if the favourite with the bookmakers, but he will be punished if he shows the hesitation and vulnerability he displayed against Zverev.
Prediction: John Isner in three