Ostapenko ends breakout year on a high with first WTA Finals win
Karolina Pliskova had already qualified as White Group winner but fell to Jelena Ostapenko, who won at the WTA Finals for the first time.
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