James Nitties hit a sparkling seven-under-par 65 to take a one-shot lead at the midway point of the Australian Open on Friday.
Jordan Spieth charged but faltered and Adam Scott moved into contention at Royal Sydney, but it is Nitties who leads the way.
The 34-year-old eagled the par-five second, his 11th hole, and mastered the gathering wind with five more birdies on the way home to storm to the top of the leaderboard at nine-under, a shot ahead of New Zealander Ryan Fox.
World No 7 Scott also blitzed the back nine for a 65 and a share of fourth place on six-under, with American Spieth a further shot back in a share of ninth after a double bogey at the 15th left him with a 70.
Australia's Rhein Gibson, who holds the record for the lowest round in golf after shooting a 55 in Oklahoma in 2012, carded 66 to take third place on seven-under behind Fox, who mixed six birdies with two bogeys for a second 68.
Asia-Pacific amateur champion Curtis Luck and Lucas Herbert, who shared the overnight lead, both shot 71 to drop to fourth with fellow Australians Scott, Rod Pampling and Todd Sinnott.
Scott got an early chance to make up for his disappointing opening round of 73 but only got into his stride on the back nine, where he picked up four birdies as well as an eagle courtesy of a brilliant four-iron approach shot at his 16th hole.
The former world No 1 was not happy with two or three short putts he missed, including a five footer at the last, but was pleased that his poor start to the tournament had spurred him into action.
"Another day around even par and I'll probably miss the cut, so there's no option but to play well," he said.
"Spending 27 holes finding [your rhythm] costs you a lot and I think it does often to me - or has this year - where I slow start but have good weekends.
"I'm very happy with 65, but I can always do better."
Spieth, Australian Open champion two years ago, started the day two shots off the pace and looked like launching an assault on the top of the leaderboard when he picked up four successive birdies from the sixth.
But the birdies dried up after the world No 5 turned into the wind for the back nine and he missed the green with his approach shot then three-putted for the double bogey at the 15th.
It was his lack of touch with the putter that bothered the twice major champion most.
"I made a six-footer today and other than that, I didn't make anything outside three feet," he said.
"I've been very much brainless putting but I'm still in contention in this tournament, so I feel like that's dangerous from our side."
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