Ashleigh Barty sealed the end-of-year number one spot with a 5-7 6-1 6-2 victory over Belinda Bencic at the WTA Finals in Shenzhen.
French Open champion Barty was made to work for victory over the course of one hour and 57 minutes in the red group against Bencic, a fellow debutant at the WTA's showpiece event.
Fresh from her Kremlin Cup triumph, Bencic was looking to build on a streak of four consecutive victories against players ranked number one in the world.
The Swiss edged a tight opening set, saving a break point with a service winner and converting the only other on offer in the penultimate game.
A pair of double faults put Barty in peril at that point, forcing her to crank through the gears in set two – combining trademark slices with crunching forehand winners.
Her serve firing emphatically, the template was set for Barty to race to glory.
The other red group encounter also went the distance as Naomi Osaka beat Petra Kvitova 7-6 (7-1) 4-6 6-4.
A re-run of January's Australian Open final did not disappoint, with Osaka outlasting Kvitova after two hours and 39 minutes to extend her winning run to 11 matches – equalling a career best.
Kvitova flew out of the blocks with a break in the first game before forcing Osaka to save two more in the third.
Now on the board, Osaka was able to banish her 0-3 return from last year's WTA Finals and get to work, breaking back for 4-4, saving three break points in the next game and breezing the resulting tie-break.
Four breaks were exchanged by the time the second set reached 3-3 but Kvitova forced a decider by taking the second set point offered to her by Osaka in the 10th game.
Kvitova's seventh and eighth double faults handed Osaka a break for 2-1 in the decider and an initiative she would not surrender.
A volley into the tramlines from the Czech put Osaka 5-2 up and, despite dropping serve in the next game, the insurance of the double break meant she was able to get over the line.