Dunlap, the 20-year-old University of Alabama sophomore and reigning U.S Amateur champion, is the first amateur winner since Phil Mickelson at the Tucson Open in 1991.

Playing in just his fourth Tour event, he became only the seventh amateur winner since 1945 – and the third since 1957.

The only amateur in the 156-player field in the tournament long known as the Bob Hope Desert Classic, Dunlap surged into a three-shot lead with a sizzling 60 in the third round.

He lost that lead on Sunday on the front nine on the Stadium Course at PGA West, but he played with the resilience of a seasoned veteran down the stretch, capped by his recovery from two errant shots on the 18th to finish with a six-foot par putt.

"Nothing like I've ever felt," Dunlap said. "It was so cool to be out here and experience this as an amateur."

He ended with a two-under 70 to finish at 29-under 259 and break the tournament scoring record as a 72-hole contest. He's also the youngest winner in the event's history, and he became the youngest amateur to win on the Tour since 1910.

Bezuidenhout birdied the 18th in the group ahead to keep pressure on Dunlap, whose tee shot landed high in the rough. His second shot was equally as erratic, but took a fortunate roll from the rough into a grassy drainage area off the green.

"It was so cool to be out here and experience this as an amateur." – Nick Dunlap.

Dunlap chipped to inside six feet with his third, and celebrated the par putt for the title with hugs from his parents, his girlfriend and his college coach, Jay Seawell, who all flew cross-country over the weekend to watch in person.

While Dunlap could celebrate one of the most impressive performances in recent golf history, he could not receive the $US1.5 million ($A2.3 million) first-place prize, which went to Bezuidenhout after the South African's final-round 65.

Dunlap also doesn't receive the 500 FedExCup points on offer but his rewards are still ample, starting with a two-year PGA Tour exemption through 2026. He can compete in full-field events even if he stays at Alabama, and he can compete in signature events if he turns pro.

He displayed incredible mental fortitude while playing through obvious nerves during the final round. His three-shot lead vanished all at once when he double bogeyed the 7th while Sam Burns made birdie, but Dunlap coolly rebounded and battled Burns down the stretch, pulling even with a birdie on the 16th.

Min Woo Lee was the leading Australian, with a closing 67 lifting him into a tie for 21st at 20-under in his first outing as a full-time PGA Tour member.