Allenby, who took a one-stroke lead into the final round, shot a five-under 66 to post a 14-under total of 270 at the Hyatt Regency course in Queensland.
"When you start with the lead all you have to do is to hold it and don't do anything stupid," Allenby told reporters. "I did what I had to do from the first hole to the last hole.
"I had some very, very tough competitors behind me and I had a lot of respect for them. So I tried to just pace myself, I tried to hit as many fairways as I could, I tried to hit as many greens as I could.
He added: "That's what I did all day, I just felt totally in control on every shot."
Allenby was flawless on Sunday, posting five birdies and while several players got to within a stroke of the lead during the final round, his third birdie of the day on the par-five 12th gave him a cushion.
He extended that advantage with two further birdies on the par-five 15th and par-four 17th holes.
"It's a nice feeling to win in that fashion," said Allenby. "It's always nice to come down the last with a four-shot lead. I was pretty consistent but to do it under the gun in the final round, that's pretty special."
(Writing by Greg Stutchbury in Wellington; Editing by Alastair Himmer)