Svetlana Kuznetsova was forced to dig deep once again as she continued her winning streak in dramatic fashion with a thrilling triumph over Karolina Pliskova at the WTA Finals.
The final player to secure a place in the Singapore field, courtesy of victory in last week's Kremlin Cup, Kuznetsova got the better of defending champion Agnieszka Radwanska in a gruelling battle to win her opening match.
And the Russian is now in pole position to qualify from the White Group after coming through a topsy-turvy encounter to beat Pliskova 3-6 6-2 7-6 (8-6) on Wednesday.
Kuznetsova was a break up on three occasions in a final set that saw both players fail to serve out the match.
Three match points then went begging for Kuznetsova in the tie-breaker, but she was not to be denied.
Victory for Radwanska over Garbine Muguruza would see Kuznetsova qualify for the semi-finals with a match to spare.
Despite struggling to land her usually potent first serve, Pliskova was a set and a break up early on, only to be undermined by increasingly frequent errors thereafter.
Kuznetsova's gutsy work in defence negated the attacking threat of Pliskova, who had begun her campaign by coming from 4-0 down in the third set to beat Muguruza.
Yet the Czech showed plenty of character to continually come from behind in the decider, before Kuznetsova finally got the job done.
Svetlana Kuznetsova  bt Karolina Pliskova  3-6 6-2 7-6 [8-6]
Kuznetsova - 24/30
Pliskova - 32/47
Kuznetsova - 6
Pliskova - 3
BREAK POINTS WON
Kuznetsova - 8/15
Pliskova - 7/13
FIRST SERVE PERCENTAGE
Kuznetsova - 59
Pliskova - 44
PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Kuznetsova - 58
Pliskova - 52
Kuznetsova - 96
Pliskova - 94