Second seed Garbine Muguruza of Spain marked her debut in the WTA finals with a 6-3 7-6 (7-4) victory over Lucie Safarova in Singapore.
The 22-year-old world number three is the first Spaniard to play in the event since Arantxa Sanchez-Vicario in 2001.
Sixth-seed Angelique Kerber beat world number five Petra Kvitova 6-2, 7-6 (7-3) for her second win in seven matches at the season-ending event.
World number one Serena Williams is absent as she recovers from injury.
Muguruza, who was beaten by Williams in her maiden Grand Slam final at Wimbledon this year, lost to Safarova in the French Open quarter-finals, the only other time they have met.