Play starts at 7.30pm
Simona HALEP (ROU)  vs Caroline GARCIA (FRA) 
Elina SVITOLINA (UKR)  vs Caroline WOZNIACKI (DEN) 
Simona Halep's Beijing Final defeat to Caroline Garcia this year was the Romanian's only reverse against the Frenchwoman. Halep had earlier beat her in Toronto this year and in Sydney last year.
Elina Svitolina has won all three previous meetings with Caroline Wozniacki, triumphing in Miami last year and also in finals in Dubai and Toronto earlier this year.
Simona Halep's best WTA Finals showing came three years ago, reaching the 2014 final where she lost to Serena Williams - having beaten the American 6-0, 6-2 in the group stages.
Caroline Garcia and Elina Svitolina are both making their debuts at the event, along with Jelena Ostapenko. Caroline Wozniacki is making her fifth appearance at the Finals - only four players have made more.
Elina Svitolina and Caroline Wozniacki entered the Finals with the most Top 10 wins in 2017, both on 10. The Latvian also leads the way in Top 5 wins, with seven.
Caroline Wozniacki "No matter who you're in the group with, it's going to be difficult. I'm excited for the challenge and excited to play the girls."
Simona Halep "I have tough opponents, for sure, but I'm here just to play my best and try to win every match I play. I didn't expect an easy group."