Late in his final round Stieger learnt he was just one shot ahead of the clubhouse leader, Queensland's Cameron Smith.
"I found out on the 15th green so I had three holes to play and I knew I had him by one shot so I just thought if I could par the last three I will win," he said.
A simple enough plan but Steiger, from NSW, admits he nearly blew it.
"On the 17th I holed a 10 foot putt for par so that was pretty good," he laughed.
Today's win is the biggest in the 18-year-old's career.
"I have won a few junior tournaments like the Jack Newton International for my age group and a few Vardons but nothing extreme like this," the scratch marker said.
"This one beats them by far."
The St Michael's member carded rounds of 70, 71, 73 and 79 to finish on 5 over 293. He finished one shot ahead of Smith and Western Australia's Ryan Peake, while Queensland's Matthew Gill placed fourth on 10 over 298.
"I found it pretty hard out there today with the pressure and the high winds and rain but in the end I got it done," he said.
"I have just found my swing recently and it has started to work for me now.
"I know after today that I will be able to handle the pressure a bit better now that I have been in the pressure and know what it is like."
Stieger is still waiting to hear from organisers whether he gets a start at the Tiger Woods led Australian Masters in November.
"Hopefully I'll be playing in the Masters later this year but if not I have been told I can go overseas next year, so I'll probably head to the US Amateur," he said.
Stieger's immediate plan is to make the NSW Institute of Sport Team. After today's great win and a 17th place at the Australian Amateur in March, the Handa Junior Masters Champion has done his chances no harm at all.
Want video tips delivered straight to your inbox? Subscribe to iseekgolf.com newsletters.