SINGAPORE - The red group began play as world no. 1 Angelique Kerber survived while Simona Halep was all business in wins at the WTA Finals  on Sunday. The 2016 Australian and US Open champion outlasted Dominika Cibulkova in a high-intensity match, 7-6, 2-6, 6-3 while Halep defeated Madison Keys 6-2, 6-4.

Kerber and Cibulkova slugged it out from the baseline for three sets in their compelling encounter. In the first set, Kerber took a quick service break advantage as Cibulkova looked to find a rhythm and shake off nerves. But it did not take long before the world no. 8 found her groove as she struck back to force a tiebreak.

In the competitive tiebreaker, it was Kerber who found the slight opening to gain the advantage, taking the set.

However, Cibulkova was not deterred as play moved into the second set and she gained control and took the momentum, riding it to even the match. But in the all-important third set, Kerber showed the poise to overcome an early disadvantage and turned the match in her favor.  After failing to hold serve early in the set, Kerber won five of the next six games to put away the Slovakian.

“I was trying to stay focused in the third set, trying to play my game and be aggressive. That was my plan and it worked well… it was a really close and really tough match,” Kerber said.

Meanwhile, Simona Halep was all-business in her victory against Madison Keys who was making her first appearance in the WTA Finals. Halep gained an early advantage against the American, who appeared to rush shots which led to numerous unforced errors in the opening set.

It was more of the same in the second set as Keys struck massive winners but gave away numerous points in her feast or famine style.  After dropping serve early in the set, she fought back to even the set at 4-4. But the 21-year old could not consolidate the break as a focused and pumped-up Halep broke back and served out the match.

“It's always the same with Madison, she's very strong and hits the ball hard so it's tough to match her power,” said Halep. “So I have to adjust, be strong with my legs and make the most of my chances.”

Play continues in Singapore on Monday as Agnieszka Radwanska faces Svetlana Kuznetsova and Karolina Pliskova squares off against Garbine Muguruza as the white group began competition.