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.