Aryna Sabalenka overcame a stern challenge from Karolina Muchova to open her WTA Finals campaign with a straight-sets victory in Indian Wells on Monday.
The second-seeded Belarusian had to work hard for the win before sealing a 7-6 (7-2), 7-5 triumph in just under two hours.
Former world No. 1 Sabalenka is bidding for her first WTA Finals title after finishing runner-up in 2022 and 2025.
The four-time Grand Slam champion appeared to be in trouble after surrendering a service break to trail 5-4 in the opening set.
However, she broke back immediately to level at 5-5 before holding her nerve in the tiebreak, winning it 7-2 to take the early advantage.
Both players struggled on serve in the second set, with Sabalenka dropping serve for the fourth time as she attempted to serve out the match at 5-4.
Sabalenka responded by breaking back immediately to move ahead 6-5 and made no mistake when serving for the match again, sealing victory when Muchova sent a backhand into the net.
"I'm just trying to win every match I play, and at the same time trying to stay in the moment and focus on my game on each point and trying to stay calm and in control," Sabalenka said afterward.
In Monday's other group match, WTA Finals debutant Mirra Andreeva swept past Ukraine's Elina Svitolina in straight sets, winning 6-4, 6-0 despite overcoming pre-match nerves.
The third-seeded Andreeva, the 19-year-old reigning French Open champion, took control with a break to establish a 4-2 lead in the opening set and never looked back against her sixth-seeded opponent.
She held serve to close out the first set before dominating the second, securing three service breaks to complete the victory.
"I was so tight, I felt I was moving like a turtle," the teenager said afterward. "I felt like I couldn't really hit the ball so I'm just very happy to get through the match and control my emotions."
Andreeva will face Sabalenka in her second round-robin match on Wednesday.
This year's WTA Finals were initially scheduled to be held in Saudi Arabia but were moved to Indian Wells in July following U.S. military strikes on Iran in February and the subsequent regional conflict.