Held at Wanneroo Golf Course, the WA Golf ranking event saw Crosby shoot 76 to win by a stroke over Derek Gardner, Ray Pigdon and Martin Minogue, who all shot 77.
Crosby attributed his maiden open victory to his putting.
‘Having only 24 putts was the key factor in the win,’ he said.
Local A-Grade golfer Ian McPherson finished fifth with a round of 78 in the top division.
Crosby’s triumph followed on from strong form at the Australian Senior Amateur Championships the previous week.
He won the 65-70 age division and finished fourth overall.