Caroline Wozniacki was back in Singapore as defending champion at the WTA Finals. However, her return ended in an opening defeat in the round robin play against the number seven seed Karolina Pliskova. Wozniacki won her opening service game but then lost five in a row, as Pliskova took the opening set 6-2. Seeded two in Singapore, Wozniacki was immediately broken at the start of the second set to hand Pliskova the advantage. Wozniacki had her moments - but she couldn't match the Czech, who saved all 10 break points she faced, including two in the final game of the match which would have seen the Dane draw level. A year ago, Pliskova was beaten by Wozniacki in the semifinals in Singapore, now she completed a 6-2, 6-4 win in an hour and 32 minutes.