Aryna Sabalenka grabbed a grueling comeback win on the opening night of round-robin play at the WTA Finals, as the No.7 seed topped No.2 seed Ons Jabeur 3-6, 7-6(5), 7-5 in Fort Worth.

Sabalenka took nearly two-and-a-half hours to take a 3-1 lead in her head-to-head versus this year’s Wimbledon and US Open finalist Jabeur, who was making her WTA Finals debut.

Jabeur was two points away from victory at 5-3 in the second set tiebreak, and she was also a point away from a 5-2 lead in the third set. However, Sabalenka stormed back on each occasion to collect the fourth win of her career over a player ranked inside the Top 2.

Sabalenka joins Maria Sakkari as the early leaders of the Nancy Richey Group after their Day 1 victories. Sakkari topped Jessica Pegula in two tiebreak sets in Monday’s first singles match.

The winner speaks: "I’m just trying to enjoy every second being here, and I’m just trying to do my best and see what the last week of the season can bring," Sabalenka said afterward.

"I was just like, ‘Keep trying, keep fighting, and make sure that if she wants to win this match, she has to do something great, not like an easy win.’ And I think that’s why I put a little bit more pressure on her and in the key moments, I was able to win it."

Return engagement: Making her second consecutive appearance at the WTA Finals, Sabalenka picked up a win in the group stage for the second straight season. In last year's round-robin portion, Sabalenka defeated Iga Swiatek, but lost her two other matches to Sakkari and Paula Badosa.

Coming into Day 1, Sabalenka had lost her last three meetings against Top 10 opposition, but those had all been against Swiatek. This time, Sabalenka prevailed to collect her 19th career Top 10 win, and her first Top 10 victory on hard court since her WTA Finals triumph over Swiatek last year.

Sabalenka was in a familiar position on Monday, as she played her 27th three-set match of the year, the most by any player on tour. By eking out the tight victory, Sabalenka nudges just over .500 to a 14-13 win-loss record in three-set matches this season.

Key moments: Jabeur broke Sabalenka twice as she raced through the first set, but Sabalenka rebounded to take a 4-1 lead in the second set. However, Jabeur battled into a tiebreak, saving a set point at 5-3 in the process.

In the tiebreak, Jabeur led 5-3 before fiery groundstrokes gave Sabalenka three points in a row and her second set point. On that occasion, Jabeur double faulted to cede the set to Sabalenka.

Jabeur took a 4-2 lead in the third set and held two break points in that game, but Sabalenka recovered to close that hold with a booming forehand, then broke Jabeur at love for 4-4.

After numerous comebacks, Sabalenka took her chance at 6-5, forcing errors from Jabeur to collect her fifth break of the match and complete the upset.

Sabalenka pulled off the win despite having 16 fewer winners and one less service break than Jabeur. However, Sabalenka was stronger returning second serves than Jabeur, winning 61 percent of those points compared to Jabeur's 51 percent success rate.

Hawk-Eye Innovations

Nancy Richey Group standings after Day 1