Nick Dunlap becomes first amateur to win on PGA Tour since Phil Mickelson in 1991

Stunning success comes after 20-year-old played in Walker Cup at St Andrews last year

Amateur Nick Dunlap shows off the trophy after winning The American Express at Pete Dye Stadium Course in La Quinta, California. Picture: Orlando Ramirez/Getty Images.

Nick Dunlap, a member of the winning United States side in last year’s Walker Cup at St Andrews, has become the first amateur to win on the PGA Tour since Phil Mickelson in 1991.

The 20-year-old, who was making his fourth appearance on the circuit through a sponsor exemption, followed a spectacular 60 in the penultimate round with a closing 70 to come out on top in The American Express at La Quinta in California.

Dunlap, who is a student at the University of Alabama, finished with a tournament record 29-under-par total, winning by a shot from South African Christiaan Bezuidenhout (65), with Justin Thomas, Xander Schauffele and Kevin Yu all a further stroke back.

"It's so cool to be experiencing this as an amateur," admitted Dunlap, who lost both his matches on the first day in the Walker Cup before picking up one-and-a-half points on day two over the Old Course.

Due to being an amateur - he’s currently third in the World Amateur Golf Ranking behind compatriot and Walker Cup team-mate Gordon Sargent and South African Christo Lamprecht - Dunlap will not receive any prize-money, with a winner’s cheque for $1.2 million going to Bezuidenhout.

Asked if he now planned to turn professional the former US Amateur champion replied: "I don't know. I have to take a second to let what just happened sink in a little bit. That's a decision that's not just about me. It affects a lot of people."

Mickelson won the Northern Telecom Open in 1991 as an amateur and turned pro the following year.