The jet-lagged world No.6 wowed fans with six birdies in the last 10 holes to power into pole position to claim her maiden national championship on Melbourne's famed sandbelt.
Green will be out early in the best of the conditions for Friday's second round looking to turn a one-shot deficit into a halfway lead.
Only South Korean amateur Hyojun Yang and fellow West Australian and her new stablemate Su Oh are above Green on the leaderboard.
Green was as much surprised with her six-under-par start, after only arriving from the US on Wednesday, as she was delighted to see Oh emerge from the golfing doldrums to grab a share of the lead.
After losing full LPGA Tour playing rights last year, Oh earned a meagre $US7414 ($A11,400) on the secondary Epson Tour in 2024 before turning to Ritchie Smith, the revered coach of Green and fellow Perth prodigies Minjee and Min Woo Lee.
"I can actually somewhat hit it somewhere where I'm looking at it," Oh said when asked how Smith had helped her after missing five straight cuts in the US.
"He's very supportive and he knows a thing or two obviously with the players that he already has.
"It's been good to like kind of rebuild and I've known Ritchie for a long time so I think that level of comfort has been there."
Su Oh tees off during the 2009 Australian Open at the Metropolitan Golf Club. (Joe Castro/AAP PHOTOS)
After playing her first Australian Open at a record young 12 years of age and rising to world No.1 amateur, Oh has now positioned herself nicely to reverse her fortunes in stunning fashion with a first victory in more than two years.
But she will have to fend off Green, her friend and foe who hopes to duel with Oh on Saturday and Sunday - by applying the pressure with another strong round on Friday.
"I'm very happy that I have an early tea time tomorrow. I'll probably get to bed early and hopefully go low again at Victoria.
"Obviously she (Oh) is my best friend so I was kind of bummed that we weren't on the same side of the draw and that we hadn't really seen each other a whole lot just yet.
"But, yeah, I'm super happy for her.
"She's obviously had a tough couple of years so a win for her this week or even just a great result will really help her going into next year's season.
"Hopefully I can, you know, be paired with her on the weekend."
First round ✅ — Golf Australia ⛳️ (@GolfAust) #AusOpenGolf Full leaderboard: https://t.co/J88MRvnQQh pic.twitter.com/nWwvHc4UeqNovember 28, 2024
Men's first-round pacesetter Lucas Herbert is off in the afternoon on Friday at Kingston Heath.
He fired an eight-under 63 at Victoria on Thursday to snare a one-stroke lead over Japanese amateur champion Rintaro Nakano and unheralded American Ryggs Johnston.
Cameron Smith was one shot further back entering his second round at Kingston Heath, which the 2022 British Open champ claimed had been deliberately set up as soft for "American style" golf.
If he takes advantage of the unusually easy set up, Smith remains the player to beat over the weekend, says Herbert.
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