The 60-year-old Stadler, who started the final round with a two-shot advantage, recovered after dropping three strokes over a four-hole span on the back nine to finish with a round of 1-under-par 71, ending the tournament at 13-under 203.
The 1982 Masters champ -- who had logged just one Top 10 finish this season in nine starts -- outpaced Fred Couples by a single shot at North Shore Country Club.
Couples had a chance to force a playoff but bogeyed the 18th for a 6-under 66, ending alone in second place at minus-12.
Charging into a share of third place at 11-under 205 was Mark O'Meara, who carded a 4-under 68.
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