LOS ANGELES (AFP) — Reigning US Amateur champion Nick Dunlap became the first amateur since 1991 to win a PGA Tour title, winning a back-nine showdown on Sunday to capture the American Express tournament.

Dunlap, a 20-year-old sophomore at the University of Alabama, sank the winning par putt from just inside six feet at the 18th hole to fire a two-under-par 70 at the Pete Dye Stadium Course — one of three courses used this week.

Meanwhile, Filipino Rico Hoey, who sizzled with a 63 laced with nine birdies in the opening round at the Nicklaus tournament layout, missed the cut of this $8.4-million championship.

Despite his victory, however, Dunlap will not take home any money from the win.

As an amateur, he is ineligible for the winner's prize of $1.51 million, which goes to runner-up Christiaan Bezuidenhout, who finished on 260 after a closing 65.

Dunlap finished on 29-under 259 to set a 72-hole record low winning score, breaking the mark of 28-under set by Patrick Reed in 2014.

"I felt this script today was already written," Dunlap said.

"I was going to give it everything I had whether I shoot 75 or 65 or 70."

Dunlap became the first amateur to win a US PGA Tour event since Phil Mickelson captured the 1991 Northern Telecom Open in Tucson, Arizona.

Dunlap also became the second-youngest PGA Tour winner in the past 90 years, trailing only Jordan Spieth's victory at 19 at the 2013 John Deere Classic.

The historic victory didn't come without tension-packed drama.

Dunlap sank a birdie putt at the par-5 16th to share the lead with 24th-ranked American Sam Burns, who found water off the tee at the par-3 17th on the day's toughest hole while Dunlap was on the green 35 feet from the hole.

Dunlap made a routine par while Burns stumbled with a double bogey and the amateur led by two with the par-4 18th remaining.

But ahead of him on the 18th green, South Africa's Bezuidenhout birdied to pull within one.

At 18, Dunlap's tee shot went way into the right rough and his approach stopped 75 feet from the hole down a slope.

Dunlap pitched his third to just inside six feet and then sank his par putt for the victory

"Nothing like I have ever felt," Dunlap said.

"It's so cool to be out here and experience this as an amateur."

"Whether I had made that or missed that, if you would have told me Wednesday night I would have a putt to win this golf tournament, I wouldn't believe you."

Sharing third on 261 were Taiwan's Kevin Yu, who matched his career-low PGA round with a 63, and Americans Xander Schauffele and Justin Thomas.

Despite missing out on the winner's check, Dunlap will become eligible to take PGA Tour membership at any time in the 2024 PGA campaign.

Then he would receive the benefits of any PGA Tour winner, which include membership through the 2026 season plus entries into the Masters and PGA Championship and any unplayed "signature" events.

Dunlap already has berths in this year's Masters, PGA and British Open from his US Amateur triumph if he is an amateur when the events tee off.