Francesco Molinari clinched an unlikely two-stroke victory at the Arnold Palmer Invitational when he stormed home with a closing eight-under-par 64 in Florida on Sunday on a day where defending champion Rory McIlroy faded in finishing joint sixth. 

The Open champion enjoyed his "best putting day ever" which he capped off by sinking a 45-foot birdie at the difficult par-four 18th at Bay Hill in Orlando.

The usually low-key Italian raised his right arm in the air with his index finger outstretched to hail his final putt.

Molinari posted a 12-under 276 total and, after a two-hour wait in the clubhouse, celebrated his third PGA Tour victory when none of the overnight frontrunners could match his total.

English overnight leader Matthew Fitzpatrick shot 71 to claim second place on 10-under.

McIlroy, despite a birdie at the second, could not get any real momentum going and had a closing round of 72 that saw him finish four shots behind the winner. It was a day to forget for Graeme McDowell as his 78 saw him in tied-54th on two over.

"I thought there was an outside chance and just started making putts," 36-year-old Molinari told NBC television about his mindset after he had teed off five strokes from the lead.

"Probably have to say my best putting round ever.

"I don't know if I could have done a lot more than that to be honest."

Asked what had elevated his game over the past year, he said confidence had a lot to do with it.

"In the summer I went through a run of golf that was hard to believe, even for me.

"The winter came and it was time to find some motivation, which wasn't extremely easy after last year. The smart thing to do was to take a long break."