Caroline Wozniacki battled through a troublesome knee complaint to earn a crucial three-set victory over Petra Kvitova in the White Group of the WTA Finals.
Defending champion Wozniacki and Kvitova lost their opening matches of the round-robin phase to crank up the importance of Tuesday's contest in Singapore.
It was Wozniacki who struck first in a tense opening set, but a problem with her left knee limited the Dane's movement and allowed Kvitova to level the match.
The see-saw nature of the match went back in Wozniacki's favour, though, and the second seed completed a 7-5 3-6 6-2 victory to end a four-match losing streak over Kvitova dating back to 2014.
Victory reignites Wozniacki's bid to reach the semi-finals, while Kvitova - who mixed 40 winners with as many unforced errors - will be eliminated should compatriot Karolina Pliskova beat Elina Svitolina.
It took until game eight for the first break of the match when Wozniacki followed up a fierce backhand with a thumping forehand winner.
The Dane failed to serve out the opener, wasting a set point in the process, as Kvitova hit back immediately and then earned another break-point chance in game 11.
That danger was quelled and, with Kvitova serving to stay in the set, Wozniacki saw another set point go missing before the third time proved a charm when the Czech put a forehand into the net.
After a break apiece to start the second, Kvitova stole in front again in game three when she correctly reviewed a ball called out and Wozniacki needed strapping on her knee during a medical timeout after game four.
A glorious deft lob briefly levelled the set at 3-3, but Kvitova quickly regained the advantage and, with Wozniacki's movement now clearly hindered, she cantered through the remaining games.
But Wozniacki gained a second wind as the momentum swung once again.
Wozniacki broke at the first time of asking with a double-backhand pass at the end of a majestic rally and, with Kvitova – who is asthmatic – visibly struggling with her breathing at a change of ends, a break of love followed to establish a 4-1 lead.
From there it was a formality for Wozniacki, who can now look ahead to her final group match with Elina Svitolina.
Wozniacki  bt Kvitova  7-5 3-6 6-2
Wozniacki - 19/14
Kvitova - 40/40
Wozniacki - 3/0
Kvitova - 2/3
BREAK POINTS WON
Wozniacki - 6/9
Kvitova - 5/13
FIRST SERVE PERCENTAGE
Wozniacki - 70
Kvitova - 59
PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Wozniacki - 62/50
Kvitova - 51/55
Wozniacki - 96
Kvitova - 84
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