Defending champion Elina Svitolina reached the WTA Finals showpiece in Shenzhen when a tearful Belinda Bencic retired injured in their semi-final.

The Ukrainian, 25, had fought back to lead 5-7 6-3 4-1 when Swiss Bencic, 22, pulled out with cramp.

Bencic took the opening set - the first dropped by Svitolina in the tournament - minutes after taking a medical timeout for a leg injury at 6-5.

The Swiss, broken twice in the second set, battled on but could not finish.

Bencic is the fourth player to suffer an injury at the women's end-of-season event featuring the world's top eight players, following the withdrawals of Canada's Bianca Andreescu, Naomi Osaka and the Japanese two-time Grand Slam champion's replacement at the Finals, Kiki Bertens.

Svitolina, ranked eighth in the world, said she was "sad" for Bencic and hoped she would recover for next season.

The Ukrainian will play Australian Ashleigh Barty or Czech Karolina Pliskova, the top two players in the world, in Sunday's final.

"I will leave everything out on court in the final to lift that trophy again," Svitolina said.