Jelena Ostapenko was in fine form as she claimed her first WTA Finals victory, inflicting White Group winner Karolina Pliskova's first defeat of the competition by prevailing 6-3 6-1.
Ostapenko was already eliminated having lost her opening two matches against Garbine Muguruza and Venus Williams, while back-to-back triumphs had clinched top spot for Pliskova.
The Latvian struggled due to a high number of errors in her previous outings but she struck a series of impressive winners to get the better of the world number three.
It ensured Ostapenko ended a breakout year in which she won the French Open in victorious fashion, while Pliskova will need to pick herself up ahead of the semi-finals.
Ostapenko saved three break points to hold her opening service game but – as she has with regularity in Singapore – failed to consolidate after winning against serve with her big shots missing.
Pliskova wilted under Ostapenko's aggression, the 20-year-old reeling off a fourth straight game to take the first set with a whipped forehand.
The Latvian was growing in confidence and went a break up in the second after a double fault from the Czech, and she did not look back from there.
Ostapenko claimed another break before serving out the match, a wide forehand from Pliskova ending the contest on the first of three match points.
Ostapenko  bt Pliskova  6-3 6-1
Ostapenko – 25/14
Pliskova – 8/17
Ostapenko – 4/5
Pliskova – 2/4
BREAK POINTS WON
Ostapenko – 1/4
Pliskova – 5/12
FIRST SERVE PERCENTAGE
Ostapenko – 49
Pliskova – 58
PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Ostapenko – 63/72
Pliskova – 57/36
Ostapenko – 64
Pliskova – 45