Dunlap finished the season-opener at 3-under 277, the highest winning score in the last 27 Nationwide Tour events dating back to last April.
His win was cemented, in part, by the poor scores of the two players who started the round in front of him.
Third-round leader Arjun Atwal had a 74 and slipped into a tie for second place with Jeff Klauk (69) at 2-under 278. Chris Smith, who held second place overnight, also shot a 74 and ended alone in fourth place at 1-under 279.
Dunlap's first win came four seasons ago at the Mark Christopher Charity Classic, where he finished ahead of two players, Bubba Watson and Scott Gutschewski, who are now PGA TOUR staples.
He made 79 starts since that tournament and this one, missing the cut as often as he made it, with just three top-10 finishes mixed in.
Dunlap said he hadn't played a round of golf since Christmas. He started the tournament with only conditional status on the Nationwide Tour.
'It's the first tournament of the year and you almost don't have any expectations,' said Dunlap. 'You come out here and you hope to play well, but you never know until the first tee. I mean, I was hitting it good on the range but you never know if that will transfer to the golf course.'
Dunlap described the conditions this week at Panama Golf Club as 'almost like [the] U.S. Open.'
Nobody knew that better on Sunday than Atwal, who had given three shots back to the field by the time he made the turn. The overnight leader's start made Dunlap's passable, though the eventual winner posted just a 1-over 36 on the front.
Dunlap, who coughed up a three-shot lead with a 73 on Saturday, went on to make two birdies and two pars on the back nine Sunday, good enough for the win.
He carried a two-shot lead to the 18th hole, then made his fourth and final bogey. The only player with a realistic shot to tie him, Atwal, posted his third consecutive par in the final group to end one back.
'To win on this golf course is very rewarding,' said Dunlap, 44. 'This essentially gives me a two-year exemption. This sets me up for the rest of the year and gets me about halfway to earning my PGA TOUR card for next year.'
Bill Lunde shot a 71 and finished alone in fifth place at even-par 280. Grant Waite (70) and Jarrod Lyle (73) were another shot further back at 1-over 281.