Aryna Sabalenka grappled with her own frustrations and a misfiring serve to begin her WTA Finals campaign with a tight victory over Karolina Muchova.

World number two Sabalenka is bidding to win the season-ending title for the first time in her sixth appearance.

With rival and world number one Elena Rybakina withdrawing on the eve of the competition, Sabalenka is arguably the favourite to triumph on the courts where she won the Indian Wells title in March.

However, neither she nor Wimbledon runner-up Muchova were consistently at their best in the first group two match.

Belarus' Sabalenka battled back from a break down in both sets to win 7-6 (7-2) 7-5.

She cut a frustrated figure at times but reined in her emotions, with her forehand in particular growing stronger as the match progressed.

Her serve, however, was inconsistent. Sabalenka produced seven double faults to four aces, but landed 59% of her first serves and won 33 of 44 points behind it.

"It was a bit tricky with the sun [and] with the shade," Sabalenka told Sky Sports.

"Sometimes I had to adjust my toss, sometimes I had to serve blind, but it's all part of the game."

French Open champion Mirra Andreeva faces Ukraine's Elina Svitolina later on Monday.

Sabalenka has had - by her high standards - a strange season.

For the first time since 2022 she has not won a Grand Slam singles title, having lost the Australian Open and US Open finals to Rybakina, and her last title came in Miami in March.

After winning just one of her three matches during the Asian swing, Sabalenka took a break before the season-ending finals.

She faced a tricky task against the crafty Muchova, who was the only player at the event to have a winning head-to-head against her.

The Czech also claimed the first break of the opening set - but, in a pattern that repeated throughout the match, Sabalenka broke straight back.

Muchova served for the first set but a string of errors forced her into a tie-break, and more mistakes gifted Sabalenka the opener.

A topsy-turvy second set featured five breaks of serve, with Sabalenka serving the match out on her second attempt.

Elsewhere, Britain's Cameron Norrie beat Australian James Duckworth 7-5 6-0 to reach the Stockholm Open second round.

Norrie will face top seed Taylor Fritz next as he continues his preparations for this month's Davis Cup Finals.

Fellow Briton Toby Samuel claimed a 6-3 6-2 win over Leo Borg - son of 11-time Grand Slam singles champion Bjorn - at the same event.