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 to reach the semi-finals.
In the second pool match on Wednesday, Poland's Agnieszka Radwanska got her title defence back on track with an accomplished 7-6 (7-1) 6-3 victory over French Open champion Garbine Muguruza, a result that eliminated the Spaniard.
After battling toe-to-toe for two hours and 17 minutes, 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 successfully defended her Kremlin Cup title on Saturday and the world number nine has shown incredible staying power to first outlast Radwanska on Monday and now Pliskova.
The victory had put Kuznetsova on the verge of sealing a semi-final spot at the year-end championships for the first time in six attempts and her berth was assured when Radwanska beat Muguruza in the late match.
After two bruising sets left things all square, and with both players emerging from three-setters on Monday, the fatigue finally kicked in and neither was capable of holding serve in the deciding set.
So after combining for eight breaks in the set, it was only fitting the match would be decided in a tiebreak.
Service woes also littered the match between Radwanska and Muguruza with three breaks apiece sending it into a tiebreak which Poland's world No.3 sealed with a spectacular backhand winner as she captured the last six points in a row.
Radwanska shrugged off an early break in the second set to overwhelm Muguruza with exceptional shot-making and brilliant service returns, closing out the 96-minute contest on her first match point with her sixth break of the match.
Radwanska and Pliskova meet on Friday with the winner advancing along with Kuznetsova to the semis.
