Starting at 5pm
Karolina PLISKOVA (CZE)  v Venus WILLIAMS (USA) 
Not before 7.30 pm
Garbiñe MUGURUZA (ESP)  vs Jelena OSTAPENKO (LAT) 
The opening day's action features both the youngest (Jelena Ostapenko, at 20 years and 141 days) and the oldest (Venus Williams, 37 years, 132 days) qualifier at this year's event. Williams is the third eldest qualifier of all time for the WTA Finals, only Billie Jean King (39 years old in 1983) and Martina Navratilova (38 in 1994) appearing at a older age.
Karolina Pliskova's three WTA titles won in 2017 (Brisbane, Doha and Eastbourne) is bettered only by Elina Svitolina's five. Pliskova leads the way this year in most aces hit (438) and is level with Caroline Wozniacki for hardcourt wins - both on 37 ahead of the Finals.
Jelena Ostapenko is the first ever Latvian to reach the WTA Finals, while the US has been represented in 42 of the 46 events.
Venus Williams is making her fifth appearance at the event, only four players have appeared more often.
Karolina Pliskova and Venus Williams are level at a win apiece in previous meetings, the Czech winning at the US Open last year after Williams prevailed in Zhuhai in 2015.
Garbiñe Muguruza has won two of her previous three encounters with Jelena Ostapenko, defeat in Wuhan this year following wins in Rome in both 2016 and 2017.
Venus Williams: "Nobody's here expecting that it's going to be an easy match. Hopefully you play your best of the season with all the matches under your belt."
Garbiñe Muguruza: "It's one of the most prestigious tournaments as only the last eight are here. I feel like we're playng a semifinals or a final. It's very exciting."