Haas, who has never won in his entire career in the state of Florida, finished 36 holes at 13-under-par 139 and is one clear at the Raven Golf Club at Sandestin.
Overnight co-leader Tom Purtzer managed a 3-under 67 and is alone in second place at minus-12. His fellow first-round leader, Eduardo Romero, was one shot worse on Saturday with a two-under 68 and came in third at 11-under- par 131.
Loren Roberts was one behind until a horrible double-bogey at the closing hole. He shot a 4-under 67 to join last week's Senior PGA champion Denis Watson (67) and Brad Bryant (67) in fourth place at minus-10.
Haas started slowly with only one birdie in his first five holes, a 12-footer at the third. He added another birdie at six, then did not collect his next birdie until the par-5 11th, when he two-putted from the fringe. That birdie got Haas to 10 under par for the championship.
At that point, Haas trailed Purtzer and Romero, who were both at 12 under par. That did not last long as Purtzer hit a horrible approach at 13 that stopped well left of the green. Purtzer bogeyed the hole to fall back to minus-11, but both he and Romero would tumble further down the leaderboard.
One hole later, Romero drove into the water and Purtzer went through the fairway on the right side. Romero could do no better than double-bogey, while Purtzer made his second consecutive bogey and now Haas assumed control.
Haas, the leading money earner so far this season on the elder circuit, hit a pitching-wedge to 6 feet to set up a birdie at the 15th. He tallied back-to-back birdies when his 35-footer at the par-3 16th found the bottom of the cup.
Haas added one more birdie when he two-putted from the back fringe at 17. He parred 18 to post his 13-under-par score.
'I probably played better today than yesterday,' said Haas, who owns two wins this season on the Champions Tour. 'I hit better shots today and managed to get it around.
'My mindset will be aggressive. I'll have to play well. The pins will be in some tough spots. I won't be thinking about not winning in Florida before.'
Purtzer rebounded from the mistakes in the middle of the back nine. He landed in the front bunker off the tee at 15 and blasted out to three feet, where he holed the birdie putt.
At the 17th, he too found the back fringe with his second and Purtzer two-putted for a birdie to get within one of Haas' lead.
'The bogeys I made were unforced errors,' said Purtzer, who has also never won in Florida in a PGA TOUR-sanctioned event. 'Anytime you're chasing Jay, it will be tough. You have to do your best.'
Mark James carded a 7-under 64 and is alone in seventh place at 9-under-par 133. David Eger (64), Mark McNulty (66), James Mason (67) and Massy Kuramoto (67) are knotted in eighth place at minus-8.