Play starts at 7.30pm local time
 Naomi OSAKA (JPN) v  Sloane STEPHENS (USA)
 Angelique KERBER (GER) v  Kiki BERTENS (NED)
Sloane Stephens and Naomi Osaka have played only once before - in 2016's Acapulco quarterfinal. The American won, 6-3, 7-5.
Both are making their WTA Finals debuts in this match. Indeed, all three of 2018's debutantes feature in the Red Group, with Kiki Bertens the other.
Osaka, the WTA World No.4, and Bertens, WTA World No.9, are competing in the event at their highest ever rankings.
Kerber and Bertens have three previous meetings on the books - two of them at Roland Garros. The German won 7-6(4), 7-6(4) this year, and the Dutchwoman won 6-2, 3-6, 6-3 two years previously. Kerber had also picked up a victory earlier that year in Miami, 1-6, 6-2, 3-0 before Bertens' retirement from the match.
Kerber made the Singapore final in 2016, losing to Dominika Cibulkova 6-3, 6-4.
The German is the only player older than 30 in the 2018 WTA Finals.
Stephens, meanwhile, has a positive head-to-head record against every member of this group. In total, she is 6-1 up against her rivals.
Conversely, the American has won the fewest matches to qualify for the WTA Tour finals, posting 33 wins in 2018.
Angelique Kerber: “I’m really excited to be back here in Singapore. It’s great to finish the year here at the WTA Finals. I think it doesn’t matter in which group you are, we are the eight best players in the world right now, so I’m feeling good and ready to go.”