Teenager Rory McIlroy closed with a five over par 77 to finish tied 59th in the MFS Australian Open.
The Holywood hotshot, 17, opened with two birdies but two double bogeys and a triple bogey seven at the fourth saw him finish on 13 over par.
Australia's John Senden took the title by a shot from US Open champion Geoff Ogilvy when he carded a seven under par 65 at Royal Sydney to finish on eight under.
As many as six players shared the joint lead at one point before PGA Tour winner Senden completed an amazing run that saw him improve by 14 shots over his final 30 holes.
Senden was two-over for the day and plus six overall after he had bogeyed the fourth and sixth holes on Saturday.
But seven birdies in nine holes saw this year's John Deere Classic winner on the US PGA Tour charge back into contention with a 67.
He then fired eight birdies - including two to finish - and just one bogey in his closing 65 to win by one.