Day wasted no time making an early assault on one of his most coveted trophies in world golf, as not even a double bogey blip on his second-last hole of the day could sour a polished five-under 66 at The Australian Golf Club.

It has him menacingly stalking surprise leader and rookie Australian professional Cameron Davis, 22, who signed for an eight-under 63 in near-breathless morning conditions around the Kensington layout.

Day carded eight birdies to wow a healthy gallery before the Spieth-led afternoon groups struggled with the gusts later in the day.

The world No.2 clawed his way to an erratic one-under 70 after draining a birdie putt on the last.

Having spoken about his desire not just to return to No.1 in the world but to dominate the sport again, Day made a good fist of that promise in his first tournament on home soil in four years.

"I think it would have been a little bit disappointing this morning if I came out and shot an even par round," Day said. "It was definitely out there to shoot a deep one.

"You almost need to come out and capitalise when there's no wind. I got 13 or 14 holes in and didn't really have to worry about [the wind] until the last four or five holes."

But the same couldn't be said for Spieth, who tournament organisers are willing towards a weekend showdown against his 2015 US PGA conqueror Day, in a field some have argued lacks serious star power outside the two obvious crowd magnets.

With Australian coach Cameron McCormick on his bag instead of regular caddie Michael Greller, Spieth mixed six birdies with five bogeys and will seek to take advantage on the reverse side of the draw on Friday morning.

"This was actually the longest I've had between tournaments since college ... so I was a little anxious to get started," Spieth said. "I had nerves to begin and my short game was a bit rusty.

"It was tremendous scoring conditions [on Thursday] morning, which we're hoping to see [on Friday]. Being seven back isn't really seven back given the difference in the waves.

"I'm not anxious about the finish of this tournament yet. We just have to kind of stay focused on the goal for the next day."

Day picked up shots on three of his first four holes and, at least in the early stages of the tournament, looks every bit the candidate to win his first Australian Open, as he predicted he was capable of doing this week.

Asked to rate his round, Day said: "I want to say it's a seven or eight out of 10. If you have the lead that's a 10 out of 10. I felt like I played some pretty good golf out there."

His playing partners Rod Pampling (-3), who broke The Australian's course record during a stunning final round two years ago, and Geoff Ogilvy (-2) weren't completely cast in Day's shadow, weaving their own bits of magic as the 30-year-old took centre stage.

Unheralded Queenslander Taylor MacDonald (-6) was two shots adrift of Davis, with Nick Cullen, Alex Edge and Day a shot further back in third.

All bar two of the top 18 players on the leaderboard - Edge and NSW Open runner-up Lucas Herbert (-4) - had morning tee times in the first round.

On his blistering start, Davis said: "Whatever the score ends up being today, I was going to be happy. For it to be that low, I'm over the moon."