Aryna Sabalenka battled past Karolina Muchova in straight sets to make a winning start at the season-ending WTA Finals in Indian Wells on Monday.
Former world No 1 Sabalenka was forced to dig deep before finally prevailing 7-6 (7/2), 7-5 in just under two hours.
Second-seeded Sabalenka is chasing her first ever WTA Finals victory after suffering defeats in the 2022 and 2025 finals.
The four-time Grand Slam champion from Belarus looked to be in trouble after conceding a break of serve to go 5-4 down in the opening set.
But she broke back immediately for 5-5 and subsequently went on to hold her nerve in the tie-break 7-2 to seize the early initiative.
Both players struggled on serve in the second set, with Sabalenka suffering her fourth break as she served for the match at 5-4 up.
Crucially though, Sabalenka responded to that stumble by breaking back immediately to lead 6-5 and she made no mistake when serving for the match again, wrapping up victory when Czech opponent Muchova netted a backhand.
"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 game, WTA Finals debutant Mirra Andreeva motored past Ukraine's Elina Svitolina in straight sets, winning 6-4, 6-0, despite overcoming pre-match tightness.
Third-seed Andreeva, the 19-year-old reigning French Open champion, took control with a break to open up a 4-2 first-set lead and never looked back against her sixth-seeded opponent.
She duly held serve to close out the first set, and then demolished Svitolina in the second set, rattling off three service breaks to wrap up victory.
"I was so tight, I felt I was moving like a turtle," the teenager said afterwards. "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 game on Wednesday.
This year's WTA Finals were scheduled to be held in Saudi Arabia but in July were moved to Indian Wells after US military strikes on Iran in February and the subsequent war in the region.