Agnieszka Radwanska rallied past an exhausted Garbine Muguruza to book a maiden appearance in the WTA Finals title match against double Wimbledon champion Petra Kvitova.
Radwanska beat Muguruza 6-7(5) 6-3 7-5 while Kvitova stunned Maria Sharapova 6-3 7-6(3) in the second semi-final.
The second semi-final pitted two former WTA Finals champions against each other and while it was shorter than the first match, Kvitova's stunning comeback from 5-1 down in the second set was equally as absorbing.
Kvitova and Sharapova, two of the strongest servers on the Tour, traded early breaks before settling into a baseline battle until the Czech edged ahead in the seventh game of the opening set.
The world number five could sniff blood and broke again in the ninth game to take a surprise lead against a player who had won all three of her round-robin ties despite arriving in Singapore short of matches after a long injury layoff.
Kvitova, however, is prone to bouts of erratic play and the confidence she exuded in the opener was replaced by uncertainty as Sharapova, who has added greater variety to her game as she has grown older, raced 4-0 ahead.
The Russian somehow contrived to hand back the double break advantage, even wasting a set point at 5-2, as Kvitova rediscovered her top form to reel off five straight games and force a tiebreak.
The 2011 champion was now in full control, setting up three match points with a booming serve down the middle and when Sharapova sent a forehand sailing over the baseline, Kvitova had completed the most remarkable of second-set turnarounds.