Kang stormed home over the closing nine holes with four birdies to shoot 69 and finish at 13 under, two shots clear of Ko and six others including Ariya Jutanugarn and Sei Young Kim.
For Kang the win ends a frustrating run in 2018 when anxiety problems often got in the way of her exceptional talent.
“I don't even know right now, to be honest,” said an emotional Kang. “I've been through so much just mental struggle that it's just been emotionally draining all year. I've had just some anxiety problems for months and months. Honestly, having Ollie on the bag changed a lot and having Butch Harmon work with me.
“The main issue has been anxiety over tee balls. People might wonder what I'm doing. I actually can't pull the trigger. It has nothing to do with the result. Having to get over that last week was incredible for me. Even on the first round one shot took me I think four minutes.
“At the end the day, I'm just so in my own way. Frustrates me. After nine holes I had a temper tantrum. He (Ollie) told me to go off to the side and we did. Hit the bag, do whatever you need to do to let your anger out and start a new nine. That's what I did.
“I'm just finally happy and just working on my game properly. Yeah. It's been a lot.”
Ko’s round saw her gain 18 positions on day four and record her best finish since her win at the LPGA Mediheal Championship in April.
Su Oh and Minjee Lee finished as the leading Australians in a share of 14th position, both losing ground over the closing 18 holes.
Sarah Jane Smith was 26th and Katherine Kirk 46th.
RULES: BALL MOVED ON GREEN
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