Lee helped herself to eight birdies – including a delightful tap-in two at the par-3 18th in driving rain – to upstage the heavyweights during Thursday's opening round in Sydney.

The 16-year-old only qualified for the championship on Monday yet now shares the lead with South Korean Jenny Shin. Major winner Jiyai Shin is in solo third at five under while Sydneysider Steph Kyriacou and defending champion Ashleigh Buhai are two shots further back in a tie for fourth at four under.

"Am I leading the Australian Open? Oh, honestly I never thought that (was possible)," Lee said.

"Hopefully I can do that for the next three days."

Even more remarkably, the Year 10 Endeavour Sports High School student almost missed her morning tee time.

Missing morning tea at school is one thing, but not your Australian Open tee time.

"I thought I was at 8.38am and not 8.28am and I've learned my lesson. I won't do that again," she said. "I was putting and my coach says, 'Rachel, you're on the tee'. So I just ran for my life."

Lee said Shin is one of her heroes and was lucky enough to play a practice round with her on Tuesday.

Tournament favourite Minjee Lee made a fighting three-under 70. PHOTO: Getty Images.

Open favourite and unrelated namesake Minjee Lee earlier mounted a spirited back-nine fightback to card a three-under 70 and keep the dream alive of her and brother Min Woo completing an historic sibling double at the $3.4 million dual-gender event.

After starting on the 10th and moving to two under through five holes, Lee seemed unsettled by a three-putt bogey on the 15th. That preceded another dropped shot on the 17th before a dreaded double-bogey on 18 dropped Lee back to two over heading to the turn.

But the World No.5 and dual major championship winner fashioned six birdies coming home, including one at the last to ice her round.

Playing alongside Minjee, Kyriacou – a member at The Lakes – used her intimate course knowledge to post a 69 to trail teenager Lee by two strokes.

Japan's Ayaka Sugihara landed the first ace of the tournament, holing out from 144 metres with a 7-iron at the par-3 11th at The Australian Golf Club.

But she could still only manage a two-over 74 to be seven shots adrift of the leader.

The highlight of Kyriacou's steady round was an eagle three at the par-5 3rd hole to go with three birdies and her only bogey on No.18.

"It was a pretty solid round," she said.

"I was pretty nervous on the first and it took me a few holes to settle in, but then as it kind of goes on everyone's just walking along and the nerves eased down.

"But it still wasn't like normal. A bit of adrenaline too. I feel like I didn't even hit it my best, so I'm going to go work on that and then hopefully (go) a bit lower tomorrow."

– Darren Walton