On a day when overnight leader Matthew Fitzpatrick and Rory McIlroy struggled at Orlando's difficult Bay Hill course, Molinari drained a 44-foot birdie putt on the 18th to shoot an eight-under-par 64 and none of the final groups could match his 12 under (276) total.

Securing his fourth worldwide victory in 10 months, Molinari beat Fitzpatrick (71) by two shots, while Tommy Fleetwood (68) Sungjae Im (68) and Rafa Cabrera-Bello (69) shared third place at nine under.

Molinari said it was among his career highlights to claim victory at the tournament formerly hosted by the late Palmer, the legendary seven-time major champion who died in 2016.

"Amazing; to be at Arnie's place, it's a tournament that I used to watch on TV when I was back home in Italy and it's a magical place," Molinari, who had to wait almost two hours before his victory was confirmed, said.

Meanwhile, Victoria’s Aaron Baddeley started the final day just two shots from the lead but faded with a 74.

RIGHT: Baddeley came within a shot of the lead early on Sunday – but he faded to finish T17th. PHOTO: Richard Heathcote/Getty Images.

The four-time PGA Tour winner came within a shot of the lead early in his round but a bogey at the par-4 9th started a poor run that included only one birdie, bogeys at the 12th and 17th, as well as a double-bogey six at the 15th.

Baddeley not only squandered a chance to claim his first PGA Tour win since July 2016 but also one of the automatic exemptions to this year's Open Championship – which are awarded to the top-three finishers not already exempt.

They went to South Koreans Im and Sung Kang and American Keith Mitchell.

Warrnambool’s Marc Leishman, the 2017 winner at Bay Hill, signed off with a respectable 70 to earn a four-under total and a share of 23rd.

The Arnold Palmer Invitational is one of the PGA Tour's most prestigious tournaments – offering a US$9.1 million (AU$12.9m) purse and a three-year exemption on Tour for the winner.

- Evin Priest, Australian Associated Press