Korda, 18, dropped in a 25-foot birdie putt on the 398-yard, par-4 18th at the Royal Melbourne Golf Club to complete her first professional victory in rainy conditions.
Korda entered Sunday with a 1-stroke lead but had three consecutive late bogeys in the final round that dropped her out of the lead. A birdie at the 17th hole, however, allowed her to reach 3-under-par 289 after 72 holes after a fourth round of 1-over 74.
That tied her with Stacy Lewis, who shot 3-under 70 in the fourth round; Brittany Linicome and Julieta, who each had 71s in the final round; and Ryu So-yeon and Seo Hee-Kyung, who each shot final rounds of even-par 73.
The six were broken into groups of three and all had pars on the first playoff hole. They returned to the 18th for a third time on the day. Ryu had a bogey and four other players had pars but Korda made her long birdie putt for the championship.