Dominika Cibulkova showed great resilience to fight from a set behind and win her WTA Finals last-four clash with White Group winner Svetlana Kuznetsova 1-6 7-6 (7-2) 6-4.
The pair were the last two players to book their respective places in Singapore, with Cibulkova reaching the semis despite winning just one match - her final outing against Simona Halep in straight sets - in Red Group.
Kuznetsova appeared to be on course for a 600th career win and a place in the final when she stormed ahead, but the Slovakian raised her game to replicate her victory over the same opponent in the semi-finals of the Wuhan Open three weeks ago.
Eighth seed Kuznetsova secured an early break by forcing an error with a backhand down the line, and she then took a 4-1 advantage with a forehand winner despite seeing two break opportunities scuppered by Cibulkova.
Kuznetsova was in complete control and a long forehand from Cibulkova handed her the opening set, but the Slovakian raised her game in the second.
Cibulkova's powerful forehand was enabling her to push her opponent around the court, and, although she failed to consolidate a trio of breaks, she sailed through a tie-break to force a decider.
Kuznetsova had insisted after her defeat to Garbine Muguruza last time out she was not struggling with fatigue despite coming through a trio of three-set matches in the round robin, and she disappeared for 10 minutes before the final set.
Cibulkova took a 2-0 lead after coming out on top in a gutsy rally, but she lost four straight games with Kuznetsova refusing to go away.
However, a double-fault from Kuznetsova tied things up at 4-4, with Cibulkova then producing a pair of expansive forehands to stave off two break points and win a game that put her one away from victory - though she had to ask her trainer what the score was upon returning to her seat.
The Slovakian's triumph was complete when her cross-court forehand clipped the net, wrong-footing Kuznetsova who sent her return long.
Dominika Cibulkova  bt Svetlana Kuznetsova  1-6 7-6 (7-2) 6-4
Cibulkova - 27/31
Kuznetsova - 27/35
Cibulkova - 0
Kuznetsova - 5
BREAK POINTS WON
Cibulkova - 6/10
Kuznetsova - 8/15
FIRST SERVE PERCENTAGE
Cibulkova - 62
Kuznetsova - 68
PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Cibulkova - 60/39
Kuznetsova - 61/40
Cibulkova - 92
Kuznetsova - 96