Stadler was playing here on a sponsor's exemption as he prepared to play next week's Nationwide Tour event at the Jacob's Creek Open Championship in Adelaide, Australia.
Second-round leader K.J. Choi only managed an even-par 72 in the final round to end alone in fifth at 15-under-par 273. Adam Scott, the 2005 champion, was one stroke further back at minus-14. He was joined there by Francesco Molinari and Ian Poulter.
Stadler flew out of the gate as he birdied the first and third, each for the second straight day, to jump to 19 under and three strokes clear of the field. Things took a turn for the worse on the fifth at The Vines Resort & Country Club.
The 26-year-old faltered to a bogey on five, then another at the sixth. Stadler fell one stroke behind O'Hern as he also bogeyed the seventh to dip to minus-16. O'Hern had birdied three of the first five holes to get to 17 under.
Stadler moved back into a share of the lead with O'Hern as he birdied the ninth. Stadler, son of former Masters winner Craig Stadler, picked up another birdie on the 10th to regain his lead. He birdied the 10th all four days.
O'Hern slipped two strokes behind Stadler as he bogeyed the 12 to drop to 16- under. Stadler parred seven consecutive holes from the 11th. O'Hern birdied the 17th to get within one of the American.
The Australian made it two straight as he also birdied the 18th to claim a share of the lead at 18 under.
Stadler ended his par run with an eagle on the 18th for the win. That was the third straight round that Stadler eagled the 18th.
Stadler claimed his first European Tour title. He has also won twice on the Nationwide Tour in the United States, and was victorious at the 2005 Centenary Argentine Open.
Fred Couples, the 1995 champion, posted a 72 on Sunday. He shared ninth place with David Diaz (70) and Gavin Flint (73) at 13-under-par 275. Chris Campbell, Ross Fisher and Shiv Kapur were one stroke further back at minus-12.