Singapore: A gutsy Sloane Stephens recovered from early embarrassment to storm past Karolina Pliskova on Saturday, setting up a mouth-watering WTA Finals decider against in-form Elina Svitolina.
The former US Open champion triumphed on Saturday against an inconsistent Pliskova 0-6, 6-4, 6-1 in one hour and 55 minutes in Singapore.
A stunned Stephens lost the opening eight games before turning things around to win 12 of the next 15.
The hard-hitting Pliskova started red hot in what loomed as a one-sided contest before Stephens fought back with relentless hustle as the Czech went off the boil.
"I just tried to stay in it and started to feel the ball better," Stephens said after the match. "I'm really proud of my fight."
It was an unexpected result after Pliskova's early domination through power and precision to blitz through the first set in 31 minutes.
She pinpointed the lines to totally rattle a flustered Stephens, who uncharacteristically made a slew of errors.
After surviving an early break point, the one-way traffic continued in the second set with Pliskova breaking in the second game against a dejected Stephens.
The humiliation ended for Stephens when she broke Pliskova's previously impregnable serve in the third game and then started to find her range.
Pliskova's first serve deserted her as a composed Stephens forced a decider and her momentum continued by capturing a break to open the third set.
Stephens rolled through against a slumping Pliskova to complete a monumental turnaround, as the former world number one fell in the semi-finals for the second straight year.
Earlier, a determined Svitolina overcame the relentless power of Kiki Bertens, continuing a dogged quest for her first WTA Finals triumph.
Svitolina outlasted the world number nine 7-5, 6-7 (5/7), 6-4 in two hours and 39 minutes to continue her bid to make amends for a lacklustre early exit last year.
Her defensive prowess wore down Bertens, who blasted 41 winners but made 63 unforced errors.
It ended a fairy tale run for Bertens, who only qualified days before the tournament when world number one Simona Halep withdrew from injury.