Third-round leader Scott Gutschewski and second-round leader Bubba Watson shared second place at 9-under-par 275. Brad Adamonis, Ryan Armour, Ricky Barnes, Kevin Durkin, Brandt Snedeker, Chris Tidland and Nick Watney finished two shots back at minus-7.
Dunlap got off to a hot start as he holed a sandwedge for eagle at the third and came right back to birdie the fourth to move to minus-10.
The 41-year-old picked up another birdie at the eighth. Around the turn, Dunlap slipped to his first bogey on the 10th at Empire Lakes Golf Club. He atoned for that error with a birdie at the 12th.
Dunlap, who owns nine international titles, faltered to another bogey at the 14th, but came back with a birdie at the next. He carded his final birdie at the 17th to get to minus-12. He parred his last for his first Nationwide Tour win.
'The scoring is generally lower on this tour and that doesn't play into my hands,' said Dunlap, who spent seven years on the PGA Tour. 'On the PGA Tour, you're going to get some golf courses where 8- or 10-under is going to be there at the end.
'I can do that. I can't shoot 26 under, or rather I don't. You never say never.'
Gutschewski double bogeyed the second. He came back to birdie No. 5, but dropped shots at the seventh and 10th. Gutschewski closed with birdies on 15 and 18 to share second place.
Watson posted one birdie and one bogey on the opening nine holes. He dropped another stroke at the 12th, but finished strong with birdies on Nos. 16 and 18 to get to 9 under.
Matt Bettencourt (67), Jeff Gove (71), Bradley Hughes (70), Jon Mills (68) and Darron Stiles (73) shared 11th place at 6-under-par 278.
Robin Byrd, Brendon De Jonge, Bob Heintz, Charley Hoffman and Troy Matteson were one stroke further back at minus-5.