American Van Pelt came into the final day with a one-stroke lead after holing a 60-foot birdie putt on the 18th yesterday [Saturday] and picked up a shot on the first today [Sunday] to set the tone for his round.
He finished on 16 under overall after carding 68 today [Sunday] to beat compatriot Jason Dufner by two shots, with first-round leader Alejandro Canizares three strokes further back in third.
"Jason and I had a great battle and played well. It definitely got tight there at the end but luckily for me I came out on top," Van Pelt told the European Tour website.
"Lake Karrinyup was a great test of golf all week. It's been a battle; the wind blew, the greens were firm and fast, and it was just a joy to play all week.
"Whenever you get a lead you want to take advantage of it so it was nice to finish one off this week."
Van Pelt demonstrated nerves of steel around the green and rolled in from 15 feet at the seventh to turn in 32, before picking up his fourth and fifth birdies of the day immediately afterwards.
He two-putted at the 15th to give Dufner hopes of catching up but Van Pelt birdied the next and another dropped shot at the 17th proved inconsequential after Dufner had bogeyed the 16th.
Paul Casey finished in a tie for fifth - alongside fellow Englishman David Howell, Scotland's Scott Jamieson and Rhys Davies of Wales - after a marvellous final round of 67.
The 35-year-old Casey has struggled for form this season after suffering a dislocated shoulder in a snowboarding accident last Christmas but is showing signs of getting back to his best and finished on eight under overall - one stroke behind fourth-placed Michael Hendry.