DeCorso finished 54 holes at 11-under 205 at Kinderlou Forest Golf Club.
England's Greg Owen fired a seven-under 65 on Saturday and moved into sole possession of second place at minus-10.
David Mathis (68) and David Miller (69) are knotted in third place at eight- under-par 208.
DeCorso began the third round with a two-shot lead and the Canadian parred his first four holes. He rolled in a 40-footer for birdie at the fifth, but parred his next four to keep his two-shot cushion.
At the 10th, DeCorso knocked his approach to nine feet and converted the birdie try. He reached the green in two at the par-five 11th and two-putted for his birdie.
DeCorso holed a clutch five-footer to save par at 12, then sank a 12-foot birdie putt at the 13th. Unfortunately for DeCorso, he needed that birdie to stay two ahead of a surging Owen.
The Englishman parred his first seven, but rattled off three birdies in his next four holes. Owen birdied three in a row from the 13th, all from inside five feet, and sank a 10-footer for birdie at 17 to get within one.
'I want to keep the momentum going,' said Owen, who lost a playoff two weeks ago at the Athens Regional Classic. 'It's been fun today. Started off a little bit scrappy, but got it going from the eighth hole onwards.'
DeCorso meanwhile found some problems when he missed the green at 15. He pitched his third to 10 feet and drained the par putt to stay one ahead. DeCorso parred the last three and will be in the final group on Sunday for the second week in a row.
Last week at the Henrico County Open, DeCorso struggled to a two-over 74 and tied for fourth. On Sunday, he will try to collect his first Nationwide Tour victory and last Sunday's slip could help him in that direction.
'My pace got awful and I knew it would,' acknowledged DeCorso. 'I'm going to try and keep my routine down. I'm only in control of myself. I'd like to shoot in the 60s and see what happens.'
Daniel Summerhays (68), Bryce Molder (69), Scott Parel (69) and Jeff Brehaut (69) are tied for fifth at minus-seven.
Brendon Todd (69), Blake Adams (69) and Marco Dawson (72) share ninth at five- under 211.