The 7-5 6-7 (5) 6-4 victory was the longest match of the tournament.
Elina Svitolina reached the biggest final of her career as she overcame Kiki Bertens in three sets to secure a place in the final of the BNP Paribas WTA Finals.
The number six seed wore down Bertens to advance with a 7-5 6-7 (5) 6-4 victory in two hours and 38 minutes in Singapore.
Svitolina broke in the fourth game to take a 3-1 lead, but Bertens immediately broke back before the Ukrainian secured the opening set 7-5 on her first set point.
Bertens battled back as she broke in the opening game of the second set but Svitolina took the tenth game to make it 5-5 before taking the set into a tie-break and Bertens levelled the match.
The pair shared breaks to start the third set before Svitolina secured the decisive break at 2-1 and served out to take the longest match of the tournament.
“It was such a tough battle today and I’m very happy I could win in the end. It means a lot to me,” Svitolina said on court after the match.
“I think physically, in the end, it was just about running and chasing every ball down. I think the level was very tough and we were both playing very good tennis. I’m very pleased that I could stay in the match and close it.”