Serena Williams, her insatiable will to win as strong as ever, regained her composure after smashing her racquet and being on the brink of defeat to beat Caroline Wozniacki 2-6, 6-3, 7-6 and reach the title match at the WTA Finals.

The world number one will face Simona Halep in Sunday's final after the pint-sized Romanian crushed Poland's Agnieszka Radwanska 6-2 6-2 in the second semi-final.

Halep also demolished Williams during the round-robin stages earlier in the tournament, setting the stage for a mouth-watering rematch with the world number one.

"Being so close and still losing, it really sucks," Wozniacki said. "But, you know, I think it was a great match. I played all I could today. I played my heart out. I fought until the end."

Meanwhile, Halep, one of the most improved players in the women's game, showed no mercy against Radwanska, breaking her serve five times and racking up 26 clean winners in her lopsided win.

Ranked 64th in the world 18 months ago, she made her first grand slam final at the French Open earlier this year and now her first WTA Finals decider in her maiden appearance at the elite event.

"I'm very excited to be in the final," Halep said. "I've played my best tennis here this week."