Green survived final-round flourishes from France's Agathe Laisne (10 under) and emerging Australian Cassie Porter (10 under) at Adelaide's Kooyonga Golf Club on Sunday.
"I like to make it really nerve-racking for myself and everyone watching," the 29-year-old Green said after producing a two-under 70 to finish 11 under.
"It was tough.
"I felt like I was hitting the clubs that I needed to hit but it wasn't perhaps actually going near the hole, so it was frustrating.
"And I knew that people could come from behind today ... just really happy to have my name on the trophy amongst all the amazing other winners."
Porter fired a flawless course-record 10-under 62, featuring 10 birdies in a stunning 15-hole stretch, to finish tied for second.
"I know as professional golfers and amateur golfers and everyone that just plays golf dreams of a day that everything just works," the 23-year-old Sydneysider said.
"And I'm very fortunate that today was that day."
Australia's Karis Davidson (six under) tied for fourth as her big-name compatriots and major winners Minjee Lee and Grace Kim struggled.
Lee signed for a one-under 71 to finish three over, while Kim made belated ground on Sunday with a five-under 67, finishing three under.
West Australian and fellow major winner Green is the first local since the legendary Karrie Webb in 2014 to lift the Open trophy.
Green joins five-time champion Webb, Jane Crafter and Jan Stephenson as Australians to win their national open.
Laisne emerged as the Green's chief challenger en route to a five-under 67.
Green and Laisne, who was playing in the group ahead of the local, were tied at 11 under for much of the back nine.
The Parisian was in danger of slipping behind on the par-3 15th hole but managed to save par by chipping in from a precarious down-slope greenside position.
Green made a break on the par-5 16th by holing a clutch 15-foot downhill putt for birdie to create a one-shot buffer.
But she then pulled her tee shot on the 17th into a large fairway bunker.
From an awkward stance, she had a dose of good fortune when her shot from the sand hit a large bunker-side bush but deflected into the fairway.
Up ahead on the 17th green - with Green sitting on her golf bag looking in the opposite direction - Laisne left a 25-foot par putt short and could only bogey.
Green also couldn't save par but held her one-stroke advantage on the 18th when she had another nervy moment: her tee shot sprayed right but bounced from a grassed bank into the fairway.
After Laisne holed a lengthy par putt, the 29-year-old Green also completed a par for a cherished victory.
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