Michael Walton, who held the lead heading into the final round at Tres Marias Residential Golf Club, carded an even-par 72 to share second place with Chris Baryla at 16-under-par 272. Peter Tomasulo shot a 62 to take fourth place at 15-under-par 273.
Mathis was seven shots back to start the day and caught fire on the front side with four consecutive birdies starting at the par-four second. He found trouble with a bogey at the 11th but countered with back-to-back birdies from the 11th.
The 31-year-old continued his fine play with an eagle at the par-5 16th and clinched his maiden title with a birdie at the par-5 18th.
'To be honest, I didn't think I had a chance today,' said Mathis. 'To win, I'm just completely perplexed. This is just awesome.'
Ryan Miller, Stephen Gangluff and Russell Surber tied for fifth place at 14-under-par 274. Brad Fritsch, Robert Hamilton and Jose Trauwitz followed at 12-under-par 276.