The country's top-ranked golfer, making his first appearance on home soil in four years, remains on track to avoid a rare winless year after igniting his Stonehaven Cup assault in testing conditions during the second round at The Australian Golf Club.

The world No.12 signed for a three-under 68, which could have been so much better if he hadn't blotted his card with four bogeys to take the gloss of seven birdies.

And in an intriguing twist to the weekend, a couple of Day's young gun compatriots, barely out of their amateur careers, loom as his biggest dangers as a quartet broke away from the rest of the field.

Victorian Lucas Herbert, 21, posted the round's lowest score after a crisp five-under 66 to lead Day (-8) by a stroke as overnight leader and first-year professional Cameron Davis (-7) staggered home on his inward nine on Friday. Anthony Quayle (-6) was in outright fourth.

Two-time Australian Open winner and world No.2 Jordan Spieth (-1) laboured through his even-par second round to be eight shots adrift of the lead.

But in a tournament where it was supposed to be about two men who have previously traded places at world golf's summit, it is Day who is looming largest as he chases a first win in the national championship.

"I haven't won this year and this could be a nice little end-of-year cap to know it wasn't such a disappointing year," Day said. "A win is a win regardless of where you are and where you play.

"I know I just don't want to win one of these, I want to win multiple Stonehaven cups. I just know how Jordan has done coming with the confidence from this event and winning two majors the next year [in 2015].

"Hopefully I've got the experience under my belt in regards to winning tournaments over in the States to try to put a bit of pressure on the guy I'm playing with [on Saturday], Lucas [Herbert]. But you know what, these guys are good."

Spieth's high-profile playing partners Matt Jones, the 2015 Australian Open hero, and Cameron Smith (both -4) will seek to burst out of the pack over the weekend after outshining the rusty three-time major winner through 36 holes.

On his margin to Spieth, Day said: "Seven strokes is obviously not enough and I'd obviously like to keep pushing forward and not see him in my rear view mirror at all.

"Right now it's kind of a three-man race. The biggest thing for me and the two other blokes is we've got to separate ourselves from the pack and if we can do that it becomes a three-man race playing against each other."

Davis, 22, didn't seem to be suffering a case of nerves on the biggest stage of his career as he touched 10-under for the tournament, but dropped three shots on the testing run home to slip back to third.

He was forced to chip backwards out of a greenside bunker on his last hole of the day, but drained a long bogey putt to limit the damage.

"In this sort of situation you've just got to put it behind you and that putt felt like a par or birdie," he said.

"This is as good as it gets and the biggest crowds I've played in front of. It just makes it a lot more enjoyable. It's nice to hit good shots and have lots of people watching rather than just yourself and your mates.

"This is where I want to be and I've got to try to make the most of it."