Maria Sakkari, aiming to improve on her WTA Finals semifinal run last year, opened the season-ending event on Monday with a straight sets round-robin victory over Jessica Pegula.
Greece’s Sakkari, ranked fifth in the world, toppled third-ranked American Pegula 7-6 (6), 7-6 (4).
Action in the Nancy Richey Group continued later on Monday at Dickies Arena with Tunisian world number two Ons Jabeur – a finalist at Wimbledon and the US Open this year – losing to seventh seed Aryna Sabalenka.
The Belarusian player came up with a 3-6, 7-6 (5), 7-5 win to begin her campaign.
In a rematch of the WTA Guadalajara final won by Pegula last week, the American and Sakkari traded six service breaks in the opening set, Pegula twice recovering a break before Sakkari put it away in the tiebreaker.
After pocketing the first, Sakkari raced to a 3-0 lead in the second set before Pegula, who survived match points to win three times this season, broke back to trim the deficit to 3-2.
Pegula saved a pair of match points against her serve in the 12th game to force the tiebreaker, the second with a stinging backhand winner.
But Sakkari sealed it on her third opportunity when Pegula’s effort found the net.
“It’s never easy against Jess,” said Sakkari, who improved to 4-2 against the American. “She’s an amazing player. She’s very confident right now. I knew it was going to be extremely tough but I fought hard and trusted my game.
“I was well-rested compared to the previous match. I’m very excited to start with a win here.”