Cameron Davis fired a superb seven-under-par 64 to snatch a one-shot victory in the Australian Open as Jason Day's challenge faded after a mid-round collapse.
Davis, the world No 1,494, had started the final round six shots behind overnight leader Day but stormed through the field to claim his first professional title with an 11-under score of 273.
Gusty and unpredictable winds once again made scoring tough at The Australian Golf Club and there were four different leaders during the final round before 22-year-old Australian Davis finally sealed victory by holing his sixth birdie putt of the day on the 18th.
Sweden's Jonas Blixt, who missed a 12-foot birdie putt on the last that would have forced a play-off, and Australia's Matt Jones, the 2015 champion, shared second place, with Day dropping down to fifth place after a 73.
Davis also qualified for The Open at Carnoustie - the Australian Open is the first of 15 events in 10 countries that will make up The Open Qualifying Series for 2018 - along with Blixt and Jones.
Former world No 1 Day, who was seeking his first victory in the event, started well with a birdie at the opening hole but dropped a shot on the third.
Day was overtaken by playing partner Lucas Herbert on the front nine and an unfortunate double bogey on the ninth - where his shot out of a fairway bunker hit the lip of the bunker, rebounded left across the fairway and into a water hazard - followed by bogeys at the 11th and 13th ended his title hopes, although he did recover with an eagle at the 14th.
Davis, meanwhile, had made stealthy progress with four birdies over the first 10 holes before recording a spectacular eagle at the par-four 12th when his approach shot from 100 yards spun back into the hole.
Further birdies at the 14th and 18th, either side of his only bogey of the day at the 16th, then saw him edge out Blixt (68) and Jones (68) to lift the Stonehaven Cup.
"I didn't know where I was, to be honest, after the third round," said Davis. "I'm just glad I did enough today to get the job done.
"To know that I can play my best golf under the most pressure you can really feel, is so good. I'm going to take that going forward for sure, and hopefully it's going to help me over the line in the future."
Australian Cameron Smith (68) took fourth place on nine under, one shot ahead of Day, while Herbert, who also toiled on the back nine in his 73, shared sixth place on seven under with Mark Brown (68).
Defending champion Jordan Spieth closed with a four-under 67, which included an eagle at the 18th, to finish eighth on six under.