Thatcher shot a 6-under 65 in the final round to end at 24-under 260, edging talented youngster Jason Day for his third career Nationwide Tour title and second this season.
He also won the Peek'n Peak Classic earlier this month.
'It was such a hard-fought day out there,' said Thatcher, who claimed $117,000 for winning one of the developmental tour's biggest events. 'There were a lot of fireworks and the fans got their money's worth.
'Jason and I stood toe-to-toe, and I'm proud of my own ability to not back down.'
Day fired an 8-under 63, closing his round with a birdie at the 18th hole to force Thatcher into making par for the win. The 19-year-old Australian posted an eagle and seven birdies Sunday to finish alone in second place at 23-under 261.
He is the Nationwide Tour's youngest player.
'It was a lot of fun out there today. It was an outstanding day for me -- and obviously for Roland as well,' said Day. 'It was hard to catch him because he played so well ... But there are a lot of positives I can take out of the week.'
Vance Veazey shot a 64 and took third place at 20-under 264, one stroke in front of Richard Swift (65), Jason Enloe (66), Martin Laird (66) and Ron Whittaker (67).
Thatcher began the day with a two-shot lead, but he had a struggle on his hands almost from the start. Day made three birdies on his first six holes to climb into a tie for the lead.
Day also drove the green at the par-4 ninth and made eagle to post a 29 on the front side.
'Every time I turned the corner I looked up and saw him knocking in another important putt,' said Thatcher. 'I had a front row seat to what he was doing. It had an effect on me and spurred me on.'
Thatcher went 6 under par during a key six-hole span from No. 6 -- a stretch of good play that included an eagle at the 10th hole. Day's 25-foot birdie putt at the 18th forced him to close with a par to cap an exciting win.
'The excitement isn't just limited to the fans because we enjoy it as well,' said Thatcher, who is now just one win from a battlefield promotion to the PGA TOUR.
'We all have a pretty healthy addiction to competition and it doesn't get any better than what we faced out there today.'