The victory makes the US golfer the first amateur to win on the PGA Tour since Phil Mickelson back in 1991.

"If you'd said on Wednesday I'd have a putt to win this golf tournament I wouldn't have believed you," 20-year-old Dunlap told the Golf Channel after becoming the second-youngest winner on the PGA Tour in the last 90 years.

"I just honestly felt this script was written. I was going to give it everything I had whether I shoot 75 or 65."

Asked about coping with the pressure over the back nine, Dunlap said: "It was like nothing I've ever felt.

"It's so cool to be out here and experience this as an amateur. I don't ever want to forget today."

The University of Alabama student sank a birdie putt at the par-five 16th to equal the lead of fellow American Sam Burns at the Pete Dye Stadium Course in La Quinta, California.

Burns then stumbled on the day's toughest hole, finding water off the tee at the par-three 17th.

At that time, Dunlap was on the green 35 feet from the hole.

He went on to make a routine par, while Burns came out with a double bogey.

The amateur took the lead with the par-four 18th remaining, while on the 18th green, South Africa's Christiaan Bezuidenhout birdied to pull within one stroke.

Dunlap pulled his tee shot into the right rough, but recovered with his approach to tap in for par and claim victory with a 72-hole record low winning score for the tournament of 29 under par, 259. He broke the benchmark of 28 under set by Patrick Reed in 2014.

Dunlap is the youngest amateur to win on the PGA Tour since 1910.

While he will not collect the 1.5million dollars (£1.18million) prize money, which instead goes to Bezuidenhout, he has secured his PGA Tour card for two years.

Last year, Dunlap became the only player other than Tiger Woods to claim both titles of US Junior Amateur and US Amateur.