Thatcher ended at 15-under 273 -- a tournament record by one shot -- to claim his second career Nationwide Tour victory, and first since 2002.
'It's been a long time since I've been in the winner's circle,' said Thatcher, 30. 'You put in a lot of hard work and energy working on your game and it's such a great feeling when it all comes together and you get a win at an event like this.'
Claxton had a 2-under 70 in the final round, unable to trim his one-shot overnight deficit to Thatcher. Already a winner this season, he finished at 12-under 276 and assumed the No. 1 spot on the Nationwide Tour money list.
Brock MacKenzie fired a 65 and finished third at 10-under 278. Scott Gardiner (71) was fourth at 8-under 280, and Brenden Pappas (73) was another shot further back at 281.
Thatcher, who beat Esteban Toledo's 2005 scoring record of 274, had five birdies and just one bogey in the final round Sunday. He made back-to-back birdies at the eighth and ninth to take a four-shot lead around the turn.
After that, he cruised.
Thatcher's win and the $108,000 first-place check moved him into fourth position on the Nationwide Tour money list -- all but guaranteeing him a top-25 finish this season and a berth on the PGA TOUR next year.
His first victory, at the 2002 Bank of America Monterey Peninsula Classic, came when he was a rookie. Thatcher moved to the PGA Tour for a couple of seasons beginning in 2004, but was back on the Nationwide Tour in 2006.
Now, at 30, he feels better equipped for a stint on the PGA TOUR.
'There's five years of maturity for one thing,' Thatcher said. 'There's a reason why most golfers peak when they're in their 30s. There's a tremendous experience level and I'm certainly a much better putter then when I was on tour last time.'
Tjaart van der Walt (73) and Kelly Grunewald (74) tied for sixth place at 6-under 282. Seven players ended another stroke further back at 283.