Mitchell closed with a three-under 67 to finish at nine-under 271 at PGA National, a stroke ahead of fellow Americans Brooks Koepka (66) and Rickie Fowler (67).

"I was trying to focus on what was going on," Mitchell said.

"My mind started wandering there a little bit at the end ... and then I hit a great putt."

Mitchell was tied for the lead after 36 holes and shared second going into the final round.

He birdied four of his final seven holes for his first win as a professional – including stints on the and Latinoamerica tours.

All he had to do for that victory and a cheque for $1,224,000 (AU$1,724,000) was hold off two of the game's best in Koepka and Fowler.

Ryan Palmer (63) and Lucas Glover (66) tied for fourth at seven under while 56-year-old Vijay Singh (70) was alone in sixth at six under.

RIGHT: Mitchell celebrates after sinking the winning putt at the 18th hole. PHOTO: Michael Reaves/Getty Images.
With the wind blowing harder than it had at PGA National all week – flags fully extended off poles in the breezes, palm fronds bending as well – the finish was obviously going to be wild.
Mitchell started his day with two bogeys, which sent his mind racing back to past attempts where he got close and had a final-round falter.

Not this time.

"I said, 'I am not letting this happen again,"' Mitchell said.

Singh, bidding to become the oldest winner of a PGA Tour event with his first win on the circuit in a decade, left a 25-foot birdie putt for a share of the lead on the par-3 15th short before his tee shot found water on the par-3 17th which led to a bogey.

Third-round leader Wyndham Clark was two shots clear when he made an uphill putt from just right of the green on the par-4 4th to get to nine under but he faded to finish tied for seventh at five under.

The best of the Australians was Matt Jones, who struggled with a closing 74 to slide back to a share of 36th while rookie Cameron Davis (73) had to be content with tied 59th.