Play begins at 7:30 p.m.
Venus WILLIAMS (USA)  vs. Jelena OSTAPENKO (LAT) 
Garbiñe MUGURUZA (ESP)  vs. Karolina PLISKOVA (CZE) 
Karolina Pliskova has a 6-2 lead in the head-to-head record against Garbiñe Muguruza, including a victory in Singapore last year. But Muguruza won their most recent encounter, at the Western & Southern Open in Cincinnati this summer.
Venus Williams has won her only meeting with Jelena Ostapenko, in the quarterfinals of Wimbledon earlier this year.
Ostapenko had an outside chance to claim the World No.1 ranking at the start of the week, but following her opening loss to Muguruza, the Latvian can no longer ascend to No.1 after Singapore.
Including stats from her opening match defeat of Williams, Pliskova leads the WTA for aces served this season – 443 aces in 66 matches.
If Karolina Pliskova and Venus Williams win on Tuesday, Pliskova would qualify for the semifinals as the group winner and Jelena Ostapenko would be eliminated (Williams and Garbiñe Muguruza would play for the second spot on Thursday).
If Muguruza and Ostapenko win, Muguruza would qualify for the semis as the group winner, and Williams would be eliminated (Ostapenko and Pliskova would play for the No. 2 spot on Thursday).
If Pliskova wins in straight sets and Ostapenko wins in three sets, Pliskova would make the semifinals. But if Muguruza wins in straight sets and Williams wins in three sets, Muguruza would enter the semis.
Any other combination of results will mean semifinal qualification comes down to Thursday’s matches.
"You always feel more relaxed coming to the next matches that you have that one win, so you don't feel that extra pressure that you have to get some wins, you know. So hopefully -- I don't know how I'm gonna feel on Tuesday, but I'm sure it's going to feel good." - Karolina Pliskova, after getting her first win on Sunday
"The first match is always one of the toughest matches, and I think it's great opportunity to play two more matches. If I play well those two matches, I can still continue the tournament." - Jelena Ostapenko, looking ahead to more round-robin play
RECAPS FROM WHITE GROUP PLAY ON SUNDAY: