South Korean amateur the shock Australian Open leader

Teenage amateur Hyojin Yang is the shock halfway leader after holding her nerve during a tension-filled Australian Open second round on the Melbourne sandbelt.

The 17-year-old South Korean turned a first-round co-lead into an outright one-shot buffer with a steely two-under-par 71 at Kingston Heath Golf Club on Friday.

At eight under, Yang's closest pursuers are fellow Korean, former world No.1 and 2013 Australian Open champion Jiyai Shin and exciting 20-year-old Queenslander Justice Bosio.

Contesting only her fourth professional tournament after a distinguished amateur career, Bosio had snatched the clubhouse lead from world No.6 Hannah Green with a birdie at her last hole in a fine second-round 69 at Victoria GC.

Now she stands two rounds away from potentially taking the Australian Open trophy back to Caboolture - a year after despairingly withdrawing on the eve of the final round with COVID-19.

Bosio had then been one under par through three rounds and in the top 10.

"Yeah, it wasn't very good, I was very upset," the 2023 Karrie Webb Scholarship winner told AAP.

"I went home after the second round and I felt just super tired and went straight to bed and then I think I had an afternoon tea time because I was playing well.

"The third morning, I woke up and I was pretty sick. Tried to battle it out on the third day. Shot a couple over.

"Then I barely slept. Woke up on the fourth morning and I was just like, 'Nah, I'll pull out', which was a hard decision.

"I ended up testing and I had COVID anyway."

After finishing tied for 11th on debut in 2022, Bosio believes she belongs among the pro ranks already, even if feeling "pretty surprised" to be just one shot off the pace.

"I know that my game is there and I have been working really hard lately but, yeah, it's just been really cool to see the hard work is paying off the last two days," she said.

Shin defied gusting winds to card a typically bogey-free five-under 68 at Kingston Heath to book a third-round date on Saturday with Green.

Australia's top-ranked golfer finished with a flurry with two birdies in a 71 at Victoria to move to seven under and outright fourth in pursuit of a maiden national championship.

"It was nice to at least finish with two par-5s and be able to get two birdies to finish on a positive note and good momentum going into the weekend," Green said.

"I've put myself in a good position for the weekend, so hopefully Kingston Heath, we don't get too much rain.

"Honestly I've heard mixed forecasts. I've heard there's going to be a little bit of rain, I've heard a lot of rain, so it really depends on that.

"But I think Kingston is already soft and so that will help us women to make lots of birdies. You still have to go low, so we'll see what happens with the rain."

Two-time defending champion Ashleigh Buhai was the day's big mover.

Playing with Green, the South African carded a 68 to surge up to equal fifth at four under.

Buhai had fallen nine shots off the pace on Thursday when she slumped to three over, but clawed her way back to even par before, like Shin, also producing a bogey-free second round.

Home hopes Steph Kyriacou and Cassie Porter and New Zealand's Hanee Song are also four under with Buhai.