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.
Revenge for Muguruza
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.
Safarova served five double faults as she succumbed to defeat in an hour and 56 minutes.
"It was a very tough match, I was very nervous as it was my first time here playing singles," Muguruza said.
"At Roland Garros she played an amazing match - I played a good match also - but this time, I don't know, I just wanted to win so much. I was fighting and concentrating very much."
Third time lucky for Kerber?
This is Kerber's third appearance in the finals but the 27-year-old German has yet to progress beyond the round-robin stage of the competition.
She raced through the first set, but looked to be in trouble in the second as fellow left-hander Kvitova was twice up a service break, but the Czech player failed to capitalise on the advantage and she served a total of seven double faults.
Kerber was broken when serving for the match at 5-4, but managed to secure victory in the tie-break, the match spanning one hour 45 minutes.
World number seven Kerber has been troubled by illness and admitted: "I feel weird. It's really tough to describe... I mean, it's just something I really can't do anything against."
|WTA Finals groups|
|Red Group||White Group|
|Simona Halep (Romania, rank 2)||Garbine Muguruza (Spain, 4)|
|Maria Sharapova (Russia, 3)||Petra Kvitova (Czech Republic, 5)|
|Agnieszka Radwanksa (Poland, 6)||Angelique Kerber (Germany, 7)|
|Flavia Pennetta (Italy, 8)||Lucie Safarova (Czech Republic, 9)|