Allenby, also the 1994 winner, took a five-stroke lead into the final round, but considered withdrawing because of the nerve problem in his right middle finger. He withdrew from an event last week and said he couldn't hold a club for days.
The four-time PGA Tour winner finished with a 4-under 284 total on the sun-baked Moonah Links course. He opened with a course-record 63 and added consecutive 72s.
The Australian two-putted for par from 10 feet on the par-5 closing hole to avoid a playoff. He had two birdies and seven bogeys in the final round.
Senden finished with a 70, O'Hern shot a 72 and Sheehan had a 73. Two-time champion Aaron Baddeley (73) was another stroke back at 2 under along with Mathew Goggin (70).
American Bubba Watson closed with a 74 to tie for 14th at 2 over. Australian star Adam Scott (74) also finished 2 over.
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