The Italian began the day five shots behind five time European Tour winner Matthew Fitzpatrick and Rory McIlroy, but the reigning Open Championship winner charged up the leaderboard thanks to a flawless eight under par round and set the daunting clubhouse target of 12 under.
However, it proved to be too much for the chasing pack as Fitzpatrick finished two shots further back in second while fellow Englishman and Ryder Cup star Tommy Fleetwood, who led at the halfway stage, and Rafa Cabrera Bello were in a tie for third at nine under.
Matt Wallace was one shot further adrift alongside McIlroy as European players dominated the final standings at Bay Hill.
“It is very special to get a win here at this place,” Molinari said. “I know I’m saying the same things but the team around me just keeps pushing me and we are not done yet, it’s as simple as that.
The 36 year old also credited the hard work in the off season for his chip in at the eighth hole, he added: “(It is) Massive, massive. I did a lot of work over the winter on my technique. The chipping is improving, it was an area where I thought it could get a little better but it is just a process.
“It’s great, but that’s why we planned the winter that we did. For me, golf is the number one priority and we work hard in the off time, especially after Christmas.
“I’ve never started the seasons too quickly, to win in two or three events is something new and hopefully it is a sign of things to come in the season.”
An opening birdie got Molinari’s charge under way before he registered another gain at the third when he dialled in his approach to seven feet to move to six under par.
He improved to seven under with a birdie at the sixth and reached the turn in 32 courtesy of a stunning chip in from the rough at the eighth.
His birdie trail continued at the 12th and 13th to move alongside Fitzpatrick at the top of the leaderboard. He got on the par five 16th in two to take the outright lead at 11 under before he holed a monster 44 foot birdie putt at the last to extend his advantage as the anxious wait for victory began.
Molinari briefly moved into a three shot lead when Fitzpatrick bogeyed at the 15th after finding a fairway bunker with his second shot to cancel out his birdie at the fourth, only to pick up a shot at the 16th to claim second place.