Kelly had entered the fourth round with a three-stroke lead, then watched it slip away.
It was the 42-year-old Wisconsin players first PGA Tour title since he won two in 2002 ' exactly 200 starts ago.
Charles Howell took advantage of Kellys mid-round stumble with one of his six birdies on 11, which gave him a two-stroke lead. But bogeys at 15 and 17 left him with a 68 on the day, and he tied for second with Rory Sabbatini (67) and Charlie Wi (68).
Steve Marino, playing with Kelly, stayed within one shot until the 18th. Instead of getting the victory or forcing a playoff, he hit his tee shot into a fairway bunker and then needed two putts. He put up his third bogey and finished at 70, tied for fifth at 276.
Kelly, meanwhile, calmly rolled his final putt about 2 1/2 feet for his 13th par on the day and the championship. Despite the seven-year title drought, Kelly said he really didnt have trouble with his nerves until his final putt on 18. He said practicing deep-breathing techniques settled him down.
His first title since claiming the Sony Open and Advil Western Open in 2002 provided Kelly with his biggest payday ever. And it netted him 500 FedExCup points, moving him to 17th in the standings.
David Toms, who won this tournament in 2001, had five birdies for a 68 on the day after a bogey on the first hole. His 276 not only tied him with Marino, it boosted him in the FedEx Cup standings and into the Players Championship.