Svetlana Kuznetsova claimed her second titanic victory in a row by outlasting Karolina Pliskova 3-6 6-2 7-6 (8-6) in a thrilling White Group encounter at the WTA Finals.
After battling toe-to-toe for two hours and 17 minutes on Thursday, Kuznetsova collapsed in a heap on the court after sealing victory on her fourth match point with a backhand winner down the line to finally break the Czech's resistance.
"With all the support of the crowd and my team, I couldn't afford to let myself and everybody down so I had to fight," twice grand slam winner Kuznetsova said.
"I haven't been at my best in recent years but something changed this year... I enjoy my game, I enjoy the crowd and I feel blessed to be playing the best players in the world."
Kuznetsova was the final qualifier for the elite eight-woman event when she defended her Kremlin Cup title on Sunday and the world No.9 has shown incredible staying power to first outlast Agnieszka Radwanska on Tuesday and now Pliskova.
The victory puts Kuznetsova on the brink of sealing a semi-final spot at the year-end championships for a first time in six attempts, with her berth assured if Radwanska beats French Open champion Garbine Muguruza in Thursday's second match.
As was the case in her win over Agneiszka Radwanska, Kuznetsova grew into the match after a slow start and grabbed her first break in the seventh game but the Czech struck back immediately to regain the initiative.
The big-serving Pliskova consolidated the break with the easiest of holds, rattling through her next service game without dropping a point as she sealed the opening set in 33 minutes.
Kuznetsova was still moving tentatively and Pliskova took full advantage to forge another break of serve in the first game of the second set but the Russian found her rhythm as her opponent wavered to stage an impressive fightback.
The 31-year-old Russian broke back immediately to prevent Pliskova from running away with the contest and then reeled off five of the next six games to send the match into a decider.
With both players emerging from three-setters on Tuesday the fatigue finally kicked in and neither was capable of holding serve, so after combining for eight breaks in the set, it was only fitting the match would be decided in a tiebreak.