World number one Angelique Kerber had to battle hard for her opening WTA Finals victory, edging out Dominika Cibulkova 7-6 (7/5) 2-6 6-3 in Singapore.
Germany's Kerber needed two hours and 17 minutes to grind to victory, admitting afterwards she had to pull out her best to prevail.
"She's such a tough opponent that I knew I had to play my best tennis," said Kerber.
"I was trying to stay positive, to play my game and just go for it.
"That was the plan and it worked well."
Kerber's victory leaves her well-placed to progress beyond the group stages at the WTA Finals for the first time, after failing to do so on her previous three appearances at the tournament.
Cibulkova could also yet progress despite defeat, while Simona Halep kick-started her Singapore campaign with a fine straight-sets win over Madison Keys.
Romanian Halep dispatched sixth seed Keys 6-2 6-4 to top her group of the round-robin stage.
"I felt very well on court today," said Halep.
"It was better that I knew her. I've played her a few times this year, and I'd won every time, so I had an advantage."
Source: PA
