Major champions Jason Day and Jordan Spieth took a back seat to Cameron Davis as the former amateur star defied the odds to clinch the Australian Open in Sydney.
Former world number one Day was in pole position to win the Open for the first time in his career having taken a one-shot lead into Sunday's final round, while American defending champion Spieth was attempting to win the tournament for a third time.
However, 22-year-old Australian Davis overcame an eight-stroke deficit to reign supreme by one shot at 11 under overall.
Davis - ranked 1,494th in the world before the event got under way - carded a seven-under-par 64 to edge Swede Jonas Blixt and compatriot Matt Jones and lift the Stonehaven Cup.
He stormed up the leaderboard thanks to six birdies and an eagle at the 12th hole as Day faltered at the Australian Golf Club.
Winner of the PGA Championship in 2015, Day saw the Open slip away after he shot a final-round 73 to finish fifth, three shots off the pace.
Day struggled on Sunday, bogeying the third, 11th and 13th holes, while he also double-bogeyed the ninth to miss out on a first title this year.
As for three-time major winner Spieth (67), the 24-year-old was never really in the mix, despite scoring in the 60s for the first time this week.
Spieth ended in eighth position following a closing four-under 67, five strokes behind Davis as he failed to finish inside the top two at the Open for the first time in four trips to Australia.