Van Pelt finished at 16-under 272 at Lake Karrinyup and earned $333,330 in the event sanctioned by the European and Australasian tours.
''We had a good battle there,'' Van Pelt said. ''We both played well.''
Dufner, a two-time winner this year on the PGA Tour, shot a 69.
Spain's Alejandro Canizares was third at 11 under after a 68.
New Zealand's Michael Hendry had a 69 to finish fourth at 9 under, and Englishmen Paul Casey and David Howell were another stroke back along with Scotland's Scott Jamieson, Wales' Rhys Davies andArgentina's Emiliano Grillo. Casey had a 67, Howell shot 71, Jamieson 68, Davies 69, and Grillo 74.