Coles finished at 10-under-par 274 to claim his third Nationwide Tour title by one shot over Bradley Hughes.
It was Coles' first victory on American soil -- the last two coming at the 2002 Jacob's Creek Open Championship in Australia and the 2004 New Zealand PGA Championship.
'I am quite happy to win on American soil,' said the 37-year-old Aussie, who won $90,000. 'That is tremendous.'
Fellow Australian Hughes, the third-round leader, managed just a 1-over 72 on Sunday to finish alone in second place at 9-under 275. Hughes had led since firing a 63 at StoneWater Golf Club on Friday.
'I don't really know what happened,' said Hughes, who posted his fifth straight top-25 finish. 'I'm actually quite happy with how I played and pretty happy with how I putted. I hit the ball close, but none of them would go in. It was just one of those days.'
Coles made two birdies on the front nine -- with a 15-foot putt at the first and a 10-footer at the ninth -- to get to 9 under around the turn. He stumbled to his first bogey when he three-putted the 10th, but got that shot back with a 30-foot birdie at the next.
Another bogey at the 13th was followed by consecutive birdies at Nos. 14 and 15, where Coles rolled in putts of 40 and 20 feet to reach his winning score.
'I putted unbelievably well,' said Coles, who had rounds of 67 and 71 before posting his consecutive 68s. 'Friday I didn't putt well, but the other three days were pretty good.'
Hughes couldn't get much going on Sunday. He had bogeys at the par-3 third and par-four 16th and a lone birdie at the par-5 fourth.
When Hughes missed a 7-foot birdie putt at the 18th, Coles had his win.
'Bradley is a great player and it will click for him again,' Coles said of his countryman. 'But I am quite happy to come out on top this week.'
Boo Weekley was the top American finisher, shooting a 68 on Sunday to end alone in third place at 8-under 276. Canadian Chris Baryla had a 72 in the final round and finished one shot further back at 277.