Lonard, in a group of five trailing third-round leader Rory Sabbatini by one stroke at the start of play, had a 20-under 268 total.
The Australian doffed his cap to the crowd, almost matter-of-factly, when his short par putt on the water-protected 18th green dropped for the win.
Lonard birdied three of the first six holes on the back nine to run away in a final round that began with 15 players within five shots of the lead.
'I hit a couple of dodgy 8-irons on the par 3s, but overall, everything else was pretty good,' Lonard said.
New Zealand's David Smail, Lonard's playing partner, shot a 68 to finish second, while three Australians were tied at 15 under, five back -- Greg Chalmers (65), Scott Laycock (66) and first-round leader Michael Sim (70).
Australians Adam Scott (68) and Adam Bland (71), were six strokes back.
Sabbatini's forgettable day finished with a bogey on 18 for a 74. He tied for 10th, eight strokes back.
'The course bit back,' Sabbatini said. 'I didn't get off to the start I wanted to and, with four holes to play, I saw that Peter had gone to 19 under. I had to force the aggression.'
The 30-year-old Lonard has always done well on the Hyatt Regency resort course. He won in 2004 after sharing the 2002 title with Jarrod Moseley when darkness forced officials to stop play after the first hole of a playoff.
'A lot of guys joked that I've really got 2 1/2 , but I'll say three for now,' Lonard said.
Last year, Lonard lost in a playoff when Nick O'Hern chipped in from the bunker on the fourth extra hole. Lonard has nine Australian titles, including the Australian Open twice, and also won the 2005 MCI Heritage on the U.S. PGA tour, his only overseas victory.
Sabbatini allowed Lonard to pull away twice when the South African bogeyed two par 3s -- the third and the 11th. Sabbatini's bogey on 13 gave Lonard a three-shot cushion.
Sabbatini and American Jason Gore, playing in the final group, had problems with the swirling wind that cranked up soon after they teed off. Both left their tee shots on the par-3 third short of the green, and both missed their par putts from about 5 feet.
Sabbatini was particularly irritated with his miss, which he pulled left of the hole. He threw his putter up in the air a few feet away from his caddie, who grabbed it before it dropped to the ground.
Gore never threatened for the lead Sunday, shooting a 75 and finishing 10 shots behind Lonard.
Fellow American J.B. Holmes shot a 67 to tie for 10th. Defending champion O'Hern's 72 left him in a tie for 20th, 11 strokes behind.