Scotland's David Law eagled the 18th as he overcame a three-shot deficit in the final three holes to win the ISPS Handa Vic Open - a first European Tour title.
The 38-year-old gave himself a putt from the fringe for a three but could only make a birdie and Challenge Tour graduate Law had a one-shot victory over Ormsby and Brad Kennedy in just his 18th European Tour appearance.
Overnight leader Wade Ormsby double-bogeyed the 17th and missed an eagle putt on the 18th to force a play-off.
"It's massive", he said. "It's not something I expected".
Around the same time a huge roar reverberated around the Barwon Heads links and it was a Scot who had caused it. David Law, 27, is an unheralded player in this part of the world, having spent five years on the secondary Challenge Tour trying to find his way on to the main European Tour.
David Law hits an iron shot on his way to a closing six-under-par 66 in Australia.
To have won today, it sort of changes things a little bit. I'll go home, reflect a little bit on things and reassess.
"We said we were going to try to finish three-two-four in the hope that we could get a top-three finish".
"Then birdie 16, par 17, and going down the last we said we need eagle".
The victory represents a remarkable turnaround on the course for Law, who was on the brink of taking on other work over the winter before winning last season's SSE Scottish Hydro Challenge and finishing 14th on the Challenge Tour.
He tweeted: "The work we do @paullawriefound is not to raise golfers to win on tour but when one of our kids does win on tour which happened today it's an wonderful feeling".
Paul Dunne and Michael Hoey finished in a share of 17th spot on ten under after rounds of 73 and 69 respectively.
In the women's tournament, French golfer Celine Boutier has hung tough to claim a two-stroke victory.
The Frenchwoman finished eight under to hold off local favourites Sarah Kemp and Su Oh, and England's Charlotte Thomas.