Purtzer overcame his own demons for the win. He led entering the final round here each of the last two years, but was unable to hold that lead either time.
'I don't understand why everything has to be so hard,' said Purtzer, who won last year's Toshiba Senior Classic. 'I've been close here a number of times. It's just great to finally win.'
Lonnie Nielsen and Craig Stadler each carded rounds of 5-under 67 to share second place at 14-under-par 202, while Graham Marsh was one stroke further back at minus-13 after a closing 65.
Tom Kite, the 2004 champion, shared fifth place at 11-under-par 205 with Mark McNulty and Gil Morgan.
Purtzer opened his final round with four straight pars and saw his lead fall to one stroke. He then birdied the par-5 fifth at the TPC of the Twin Cities to get to minus-13. After a birdie at the seventh, he bogeyed No. 8.
The 53-year-old got that stroke back with a birdie on the ninth to make the turn at 14-under before he picked up another birdie on the par-4 11th.
Purtzer, who tied Don Pooley's course record of 63 on Friday, stretched his lead more with a birdie on the par-4 14th. He stumbled to a bogey at the next, just his third bogey of the week, to slip back to 15-under and closed with three straight pars for the win.
Nielsen got off to a quick start with birdies on the first and third to move to minus-11. After four straight pars, he ran in his third birdie on the par-3 eighth.
The 52-year-old struggled to his only bogey on the 10th. Nielsen parred his next six holes, before closing with a flourish. He birdied the 17th and eagled the par-5 closing hole to get within one of Purtzer.
Stadler moved to 10 under with a birdie on the par-5 third. The reigning JELD-WEN Tradition champion sank back-to-back birdies from the sixth to get to 12 under.
The 52-year-old tripped to a bogey on the eighth, but he got that stroke back with a birdie on the par-5 12th. Stadler then birdied 14 and closed with a birdie on 18 to fall one shot shy of Purtzer.
Bruce Lietzke, the 2001 champion here, ended at 10-under-par 206. He shared eighth place with Morris Hatalsky, Bruce Summerhays and D.A. Weibring.
Dana Quigley and Andy Bean were one stroke further back at minus-9.