Tunisian second seed Ons Jabeur loses on her WTA Finals debut after Aryna Sabalenka retaliated to win on the opening night of the season-ending event.
Wimbledon and US Open finalist Jabeur was defeated 3-6 7-6 (7-5) 7-5 by Belarusian seventh seed Sabalenka.
Earlier, Greek fifth seed Maria Sakkari opened the singles tournament, which presents the eight best players of the year – by beating Jessica Pegula.
Sakkari won 7-6 (7-6) 7-6 (7-4) against the American third seed in Texas.
The finals, which also sees the top eight teams of 2022 play in doubles, are being held in Fort Worth this year and there was a sparse crowd on the opening day.
Poland’s world number one, Iga Swiatek and American 18-year-old Coco Gauff play in the singles on Tuesday, opening their bids for the trophy against Russian eighth seed Daria Kasatkina and France’s Carolina Garcia respectively.