SHENZHEN — Holder Elina Svitolina sealed a place in the final of the end-of-season WTA Finals on Saturday as injury forced Switzerland's Belinda Bencic to retire midway through the third set of their semifinal at Shenzhen Bay Sports Center.

Seventh-seeded Bencic conceded defeat due to a nagging hamstring problem while trailing 5-7, 6-3, 4-1 having forced Svitolina to drop a set for the first time in the tournament.

While the Ukrainian, seeded eight, responded in style to claim the second set, Bencic's back and hamstring problems eventually saw her concede defeat and leave Svitolina's hopes of claiming the $4.75m first prize at the $14m event intact.

"You never want to finish the match and see your opponent retiring," said Svitolina. "It's very tough I think for her, and especially at the end of the season in one of the biggest tournaments and you want to play well.

"It's very sad but hopefully she can recover and be strong for next year."

Svitolina showed her intent in her first service game, firing down three aces to win it before the pair traded breaks midway through the set.

The first set looked destined to go to a tiebreak, with Bencic closing out the penultimate game with an ace before taking a medical time out to have treatment on her back.

The delay caused Svitolina to struggle at the resumption, eventually losing her service game and the first set as Bencic moved her around the court before hitting the winning point.

It was the first set the Ukrainian had lost at this year's WTA Finals but she broke immediately at the start of the second set and consolidated her position to take control as Bencic – who also required on court treatment for a problem with her right foot and hamstring – started to struggle.

Svitolina broke again in the final game to secure the second set, swatting Bencic's second serve into the far corner to level the scores and take the semi-final into a deciding set.

The 22-year-old Swiss's problems continued, however, and, with Svitolina winning four of the first five games of the third set, she conceded defeat to become the fourth player to withdraw from the tournament due to illness or injury this week.

Svitolina will face either Australian top seed Ashleigh Barty or Karolina Pliskova in Sunday's final, with the pair playing later on Saturday.

"When I was coming to this tournament, I was expecting very, very tough matches," said Svitolina.

"It's the last tournament of the season and tomorrow is the last match of the season, finally.

"It's going to be a tough one but I'm going to leave everything on the court to try to raise the cup again." — Reuters