Defending champion Elina Svitolina has maintained her unbeaten record at the WTA Finals in Shenzhen to secure her place in the semi-finals in Shenzhen.

Svitolina backed up her victory over Karolina Pliskova in her opening round-robin match with a 7-5 6-3 success over Wimbledon champion Simona Halep on Wednesday night.

“I was playing very solid today, my defence was very good and I’m very happy about that,” Svitolina said.

“Definitely I was expecting tough matches here when I arrived. I had to stay really focused from the beginning of each match. Hopefully I can keep up this level.”

The Ukrainian is the only player in the elite eight-woman draw yet to win a title this year, but could be saving her best event for last.

Svitolina has now won eight straight matches at the past three season-ending championships, including her unbeaten run to the title last year, and has yet to drop a set this week.

She will top the Purple Group with another win in her last remaining pool match on Friday night against US Open champion Bianca Andreescu.

Halep, who defeated Andreescu, drops to 1-1 before her final round-robin match against Pliskova.

Andreescu and Pliskova will look to open their accounts in Wednesday night’s second encounter, with the loser facing likely elimination from the $US14 million season finale.