Elina Svitolina got her title defence off to a winning start at the WTA FInals in Shenzhen ©Getty Images

Elina Svitolina won a marathon tie-break on her way to beginning the defence of her title with victory over Karolína Plíšková at the Women's Tennis Association Finals in Shenzhen.

The Ukrainian eighth seed held off Plíšková to claim the opening set after a tie-break which lasted for 18 minutes at the Shenzhen Bay Sports Center.

Svitolina broke the Czech's serve in the seventh game of the second set before wrapping up a 7-6, 6-4 triumph, her eighth successive win at the WTA Finals.

Victory for the 25-year-old saw her get her campaign in the purple group off to a winning start.

"That was probably one of the longest tie-breaks I have played," Svitolina said.

"I was just trying to be ready for her big serves today. 

"I tried to move quickly and react quickly. 

Romania's Simona Halep recovered from a set down to beat Canada's Bianca Andreescu ©Getty Images
Romania's Simona Halep recovered from a set down to beat Canada's Bianca Andreescu ©Getty Images

"The slightly slower surface gave me a bit more time.

"It's a big privilege to return to this event. 

"I still can't believe I won it last year."

Romania's Simona Halep fought back from a set down to beat US Open champion and world number four Bianca Andreescu of Canada in the second match of the day.

Halep, the world number five, recovered to clinch a 3-6, 7-6, 6-3 success in a thrilling purple group contest.

The top two players from each group will qualify for the last four.