'You just have to go out and play really good golf when you are that far back,' said Walker. 'I never thought I had much of a chance entering the round. You just have to catch some breaks and I did that today.'
Rick Price closed with a 68 to take second place alone at 15-under-par 273. Charley Hoffman followed at 14-under-par 274 while Jon Mills finished four shots off the lead at 12-under-par 276.
Robert Garrigus, who held a six-shot lead at Le Triomphe heading into the final round, collapsed with a 6-over 78 to join Justin Bolli in a tie for fifth at 11-under-par 277.
Walker, who captured the season-opening BellSouth Panama Championship earlier this year, had little to lose on Sunday and began his charge with four birdies over his first nine holes to make the turn at 13 under.
The 25-year-old dropped a shot with a bogey at the 13th but came right back to birdie the par-5 14th.
Walker then finished with a flurry of birdies for his second career title. The Baylor University grad birdied each of his last three holes to complete the low round of the day.
'Making a birdie putt on the last hole is overwhelming,' said Walker, who needs one more victory this season to receive a promotion to the PGA Tour. 'That is what most golfers dream about. It was probably the best feeling in golf I've ever had.'
Price, who was in search of his first career victory on the Nationwide Tour, had a bogey-free round with four birdies to finish one shot back.
Garrigus struggled early with a bogey on the opening hole. He responded with a birdie at the second but found trouble again with a double bogey at the par-3 third.
The 26-year-old dropped another shot with a bogey at the sixth but redeemed himself with an eagle at the par-5 seventh to maintain a three-shot advantage.
Things fell apart for Garrigus on the back side however where he stumbled with a triple-bogey and two bogeys to finish five shots back.
D.J. Trahan, Darron Stiles, Craig Lile, Steve LeBrun, Scott Gutschewski and Mike Springer tied for seventh at 10-under-par 278.
Charles Warren shot a 1-under 71 to finish one shot further back at 9-under-par 279 alongside Boo Weekley and Jim Rutledge.