Dana Quigley posted a 70 to take second place at 6-under-par 210. Wayne Levi, who shared the 36-hole lead with Thorpe, managed a 1-over 73 in the final round to join Mark Johnson in a tie for third at 5-under-par 211.
The 56-year-old stumbled to a bogey at the par-3 11th and fell back to 6 under with a bogey at the very next hole when he three-putted from 20 feet.
'I didn't get down on myself,' said Thorpe. 'I thought this was a course I could win on.'
Thorpe responded at the par-4 14th, however, with the first of three consecutive birdies to pull away from the pack. Thorpe then closed out his round in style with a birdie at the par-5 18th to cap off his first win of the season.
'I knew coming in I was playing pretty decent,' said Thorpe. 'The key was to stay patient today. My caddie told me to get in gear and I hit some good shots coming in.'
Quigley was on fire early with an eagle at the par-5 second and a birdie at the par-4 sixth. He struggled with back-to-back bogeys from the eighth, however, to make the turn at 5 under.
Quigley came back with a birdie at the par-5 10th, but he dropped a shot with a bogey at the 12th. He recovered with a birdie at the following hole and parred his way in to finish four shots back.
'Dana's my closest friend out here,' said Thorpe. 'If I couldn't win it, I would've wanted him to win.'
Curtis Strange carded a 1-under 71 en route to his best career finish on the Champions Tour. Strange finished alongside Bruce Fleisher and Brad Bryant at 4-under-par 212 in a tie for fifth.
Mark James finished alone in eighth place at 3-under-par 213. Craig Stadler, Morris Hatalsky and Graham Marsh followed at 2-under-par 214.