She shot 69 on the day to finish 10 under, but she was always chasing once she went par-par on the opening two par-fives to Ko's birdie-birdie.
The other contenders fell away, with compatriot Shin Ji-yai dropping back two shots on the day, while Emma Talley of the U.S. gave back four.
Ko triumphed in a co-sanctioned event previous year when not a full card-carrier and has also won 10 times on the Korean tour.
Ko, 22, left everyone in her wake with a wire-to-wire victory that franks her win in her native country previous year, a triumph that allowed her to take up full LPGA Tour membership for 2018.
Ko, who earned LPGA membership when she won the KEB Hana Bank Championship last October, was impressive start to finish at Kooyonga Golf Club, leading wire-to-wire.
Ko Jin-young ignored persistent screeching by a flock of sulphur-crested cockatoos on Sunday to record an emphatic wire-to-wire victory at the Handa Women's Australian Open in Adelaide.
"Did you see Dean's face, really scary", she said at the victory presentation on the 18th green, eliciting a roar of laughter from onlookers. She had the cushion of a four-shot lead, so that helped.
Seko: Japanese steel has no impact on United States security
Countries "should not take a beggar-thy-neighbor approach by unilaterally imposing trade restrictions ", Wang said. Other options would impose high tariffs or quotas on steel and aluminium imports.
In four rounds Ko only missed 11 greens, the best result in the field.
"The others have all been in tournament play but I have never got anything for them, let alone a Genesis", she said.
Green was outright third and had nothing to be ashamed of her first appearance in the final group at her national Open.
Australians Hannah Green, playing with Ko in the final group, Katherine Kirk and Minjee Lee are tied for third at seven-under.
Ko hit three birdies and three bogeys across a frustrating round of golf, in what appears to be a continuation of her 2017 woes.
"I couldn't have asked for a better start", she said.
She had nine birdies for the day, two bogeys and shredded the more hard back nine in 31 shots, with five birdies in the last six holes.