Poland's Agnieszka Radwanska beat Garbine Muguruza 6-7 (5-7) 6-3 7-5 on Saturday to reach the final of the WTA Finals in Singapore.
The world number six made the decisive break in the 12th game of the third set to finally break the Spanish world number three's resistance.
Radwanska, 26, will face either five-time Grand Slam winner Maria Sharapova or Petra Kvitova on Sunday.
It will be Radwanska's first final at the event in her seventh appearance.
"It was a great match from the beginning to the end, lots of ups and downs, so many rallies and a lot of running," Radwanska said.