Istanbul - World No 1 Caroline Wozniacki survived a scare and a two-hour, 39-minute battle in the WTA Championships before she scored a win here on Tuesday which carried her a long way towards preserving her top-ranked status.
The top-seeded Dane went a set and a break of serve down before getting the better of Agnieszka Radwanska, the in-form Pole, by 5-7, 6-2, 6-4 in a tortuous tussle of containment and counter-attack.
Wozniacki now needs to win just one more group match and reach the final of the season-end event, and she will be assured of being year-end world No 1 for the second successive year.
However there is no doubt that Wozniacki is keen to win this tournament, which would be her biggest so far, perhaps to use it as a stepping stone towards the first Grand Slam title of her career.
"I believe if I keep doing the right things, the outcome that I want will come," Wozniacki said.
"It’s a question of keeping your focus right and the results will look after themselves."
However, there were important moments when she called upon her father-coach Piotr to help work out how to overcome the durable and thoughtful Radwanska, the winner of 11 successive matches and back-to-back titles at Tokyo and Beijing to become the tournament’s last qualifier.
He came courtside after Wozniacki had gone an early break down, and she responded to recover from 2-4 to 4-4 with steady pressure, a few more net approaches, and some changes of pace with down-the-line driving.
But after Radwanska saved three successive set points at 4-5 love-40 it inspired her to lift her level, to take ten out of 11 points and to snatch the opening set.
Piotr was summoned again when Wozniacki dropped serve to go 1-2 down in the second set, at which stage matters were beginning to look grim. But then the match took an important twist.
Radwanska played an uncharacteristically poor game to drop serve, thumping the ball into the ground in anger, and going on to lose four games in a row before calling the trainer.
That brought some swivelling exercises for the upper body and a large patch of criss-crossed taping on her right shoulder. Her long sequence of matches seemed to be taking its toll.
Despite that Wozniacki found it hard to press home her advantage, missing three points for a 5-2 final set lead and allowing Radwanska back to 4-4 before making the decisive thrust.
That came after the Pole had saved one match point and reached a point for 5-5, when Wozniacki played a loopy, slow-ball forehand on the second match point, and saw Radwanska strike it into the net.
Earlier on Tuesday, Wimbledon champion Petra Kvitova made a good start to her hopes of winning the second biggest title of her career, when she overcame Vera Zvonareva, the former runner-up, by 6-2, 6-4.
Results from first day of season ending WTA Championships on Tuesday (x denotes seeding):
Caroline Wozniacki (DEN x1) bt Agnieszka Radwanska (POL x8) 5-7, 6-2, 6-4
Petra Kvitova (CZE x3) bt Vera Zvonareva (RUS x6) 6-2, 6-4
Samantha Stosur (AUS x7) bt Maria Sharapova (RUS x 2) 6-1, 7-5