Defending champion Elina Svitolina beat Simona Halep to become the first player to secure a place in the semi-finals of the 2019 WTA Finals in China.

The Ukrainian world number eight won 7-5 6-3 in Shenzhen to guarantee progression with one group game left.

Halep plays Karolina Pliskova in her final game and can still go through.

Svitolina will top Purple Group if she wins her final match against Bianca Andreescu, or if Pliskova beats Andreescu later on Wednesday.

Svitolina and Halep were well matched for large parts of the gruelling match but Svitolina was more consistent at crucial moments.

After a tight first, set she broke serve to love at 6-5 to take a 1-0 lead, helped by errors off the racquet of her Romanian opponent.

World number five Halep broke early in the second set, but Svitolina hit back immediately and then broke to love again to move 5-3 in front as Halep faltered.

Svitolina had to save two break points when as she served for the match - but eventually clinched the win on her first match point.