Karolina Pliskova has earned a revenge win over Caroline Wozniacki at the WTA Finals with a convincing 6-2 6-4 result in Singapore.

The 26-year-old lost to Wozniacki in the semi-finals of the tournament last year before the Dane went on to lift the Billie Jean-King trophy.

"Always tough matches against Caroline for sure," Pliskova said on Sunday.

"It was a very good match last year, the first set I think was an hour, so I gave my best today. It's always tough to defend a title, especially here, so I think Caroline was nervous but I was very happy with how I played."

Wozniacki was clearly off her game on the opening night of this year's season-ending tournament as the reigning Australian Open champion found herself chasing the match after she fell behind early.

Pliskova raced to a double-break 4-1 lead before capping the first set with a powerful service after 36 minutes.

The Czech world No.8 then broke in the opening game of the second set and unleashed a fine forehand winner for a 2-0 lead.

Wozniacki saved two match points against her serve at 5-3 down but her defeat was confirmed when Pliskova battled back against two break points to wrap up the win with an ace after one hour and 32 minutes.

Earlier, Elina Svitolina outplayed Petra Kvitova for a dominant 6-3, 6-3 victory in the opening round robin match of the WTA Finals.

"It's very nice to be back in Singapore and I'm very pleased with the performance," said Svitolina.

"I had to stay focused and stay strong mentally. I think that was the key."

All four women make up the white group and they each have two matches left to decide the top two women after the round-robin format.

They will advance to meet the top two women in the opposite red group before the WTA Finals champion is crowned next Sunday.

US Open champion Naomi Osaka will open Monday's play for the red group against Sloane Stephens before Germany's top seed and Wimbledon champion Angelique Kerber takes on Kiki Bertens of the Netherlands.