'You never really know when your last win might be your last,' said Nelson. 'I've been playing well and I've been close.'
Doug Tewell was in position to win but he bogeyed each of his last two holes for a round of 69. Tewell was joined by Jim Dent in a tie for second at 7-under-par 209.
Nelson's last victory came at the SBC Championship in October of 2001, a year in which Nelson visited the winner's circle a total of five times. He went winless in 2002 and had two runner-up finishes earlier this season before battling through injuries over the summer.
Nelson began the day in a tie for first with Jay Sigel and scattered two birdies and two bogeys on the front nine at Hayfields Country Club to make the turn at 7 under, despite suffering a bee sting on his finger on the ninth hole.
'I can't remember getting stung in a round before,' said Nelson. 'Finger hurt every time I fixed my ball mark.'
What had been a crowded leaderboard at the start of the day gave way to a logjam in the race for the top spot. Nelson persisted and reached 8 under with a 25-foot birdie at the par-3 11th.
Nelson then picked up the decisive birdie at the par-5 16th after his third shot from the sand stopped 15 feet from the cup en route to his 17th career victory on the elder circuit.
'I knew today was going to be difficult,' said Nelson. 'Guess I outlasted everyone today.'
Nelson pocketed $225,000 for the win.
'Winning helped alleviate the pain from the bee sting,' he said.
Tewell started the day in a tie for sixth and picked up two birdies on the front side to make the turn at 6 under.
The 54-year-old caught fire on the inward half with a birdie at the 10th and another at the 13th. Tewell then surged into the lead at 9 under with a birdie at the 15th before the late blunders dropped him back into a tie for second.
'I played well and I'll get over it,' said a disappointed Tewell. 'Maybe I'll win next week.'
One day after almost shooting his age, Dent collected three birdies and two bogeys for a 1-under 71 on Sunday.
Sam Torrance made his Champions Tour debut in style with a final-round 68. The former European Ryder Cup captain from Scotland finished alongside Sigel and Ireland's Des Smyth at 6-under-par 210.
Dana Quigley, Bobby Wadkins, Walter Hall, Bobby Walzel, Wayne Levi, Isao Aoki and Tom Purtzer tied for seventh at 5-under-par 211.
Tom Jenkins and Bruce Fleisher were one shot further back at 4-under-par 212. John Bland and Ed Fiori followed at 3-under-par 213.