DeChambeau began the final day at Ridgewood Country Club with a four-shot lead and closed with a two-under-par 69 to finish at 18 under and four shots clear of runner-up Tony Finau (68).

Australian Cameron Smith (69) and Billy Horschel (68) finished in a tie for third at 13 under with Adam Scott (69) a shot further back in a share of fifth.

DeChambeau was seemingly in cruise control, opening with two straight birdies which allowed the 24-year-old to weather two bogeys on the front nine.

He threw the hammer down with back-to-back birdies at the par-4 12th and par-5 13th and never looked back as he secured his second PGA Tour victory of the year and third of his career.

Securing 2,000 points and a $1.6 million ($A2.2 million) cheque for his win, DeChambeau moves into the No.1 position on the FedEx Cup playoffs rankings with three events remaining in the lucrative series.

RIGHT: Cameron Smith was the highest-finishing Australian and claimed a share of third. PHOTO: Andrew Remington/Getty Images.

"It's amazing; this one (win) is different," DeChambeau said.

"I had to grind out a couple shots at the end because I had some nerves.

"Not really knowing what to do under the gun with a tremendous lead, it was a big learning experience for me."

Queenslander Smith birdied the 10th hole to pull within three shots of DeChambeau but that was as close as he got to the American.

Scott never threatened, particularly when he dropped shots at the 8th and 9th holes.

But he rallied with a birdie and an eagle on the back nine to register his second consecutive top-five result on tour after a third place at the US PGA Championship.

Jason Day carded a lacklustre even-par 71 to finish with an eight-under total at the event he won in 2015.

Marc Leishman signed off in style with a 67 elevating the World No.18 to five-under, while 14-time major winner Tiger Woods finished at four under courtesy of a 70.

- Evin Priest, Australian Associated Press