Having turned Professional less than two months ago, the victory comes in only the rookie Professional's sixth PGA Tour of Australasia tournament.
Prior to today's result Stieger, who turned Professional for the WA Goldfields PGA Championship in October, had planned on trying to pre-qualify for next week's national open but will instead enjoy a day off.
"I don't have to pre-qualify in the morning which is a massive bonus!" said Stieger, who now has a two year exemption on the PGA Tour of Australasia and OneAsia.
"I was a bit worried about getting into next week and then the PGA. Everything was still up in the air for the next year and I didn't know where I was heading, so to come out with a win just solves a lot of problems."
Playing with the composure of a seasoned Professional, 21 year old Stieger didn't drop a shot all day at Mt. Broughton as overnight leader, amateur Callan O'Reilly, struggled to stay in touch.
"11 was a massive turning point. He made double, I made eagle and Daniel Nisbet missed a six footer for birdie."
"But I didn't lose a ball all week which was massive. I just kept it in play and not once did I hit it in the thick stuff. It was just plod along, stay patient. I holed a couple of putts and before I knew it I had a three shot lead."
Fellow rookie Professional Daniel Nisbet finished in second position at 12-under par while South Australia's Nick Cullen surged up the leaderboard on the final day to take third.
New Zealand's Ryan Fox and Kyle Grant shared fourth at 10-under and Callan O'Reilly joined Sweden's Thomas Petersson and Daniel Popovic in sixth at 9-under.
With a 7-under 65 Chris Gaunt shot the round of the day to finish at 8-under in ninth alongside Craig Hancock and Anthony Summers.