The victory makes Dunlap the first amateur to win on the PGA Tour since Phil Mickelson back in 1991. At 20 years old, he is the youngest winning amateur since 1910.

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

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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.

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 of 29 under 259.

He broke the benchmark of 28 under set by US golfer Patrick Reed in 2014.

"Nothing like I've ever felt," Dunlap said of his winning putt on the 18th.

"It was 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 (on) Wednesday night I would have a putt to win this golf tournament, I wouldn't believe you."

The 20-year-old added: "Everybody's got doubts.

"I probably had a thousand different scenarios in my head of how today was going to go, and it went nothing like I expected. I think that was the cool part about it. That's golf."

While he will not collect the £1.18m ($1.5m) prize money, he now has a PGA Tour exemption through to 2026.

The winning prize money instead goes to second-placed finisher Bezuidenhout.

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

'Most nervous I've ever been, by far'

In an emotional interview on the 18th green after sinking the winning putt, Dunlap said: "I told Hunter [Hamrick, his caddie] we hadn't faced much adversity yet and hitting that ball in the water on seven tested everything I had.

"I missed a couple of putts that I thought I was going to make. I went over a scenario for today probably a million times and it's never going to go how you plan, and it didn't. I'm so happy to be standing here [having won].

"Honestly, I felt this script today was already written. I was going to go give it everything I had. Whether I shot 75 or 65 or 70, I was going to go give it everything I had.

Asked how aware he was of his one-shot lead coming down the 18th, Dunlap replied: "I wasn't! I thought I had a two-shot lead.

"Our line was almost right of the green, it was like 'don't hit this in the water'. Then obviously I think I hit somebody - so I'm sorry to whoever that was - but got a great break and was able to get myself a good look."

He later added in the press conference: "Most nervous I've ever been, by far. Just tried to breathe, but also look up and enjoy it a little bit. It's a really cool spot to be in as an amateur and just to be here and be given the opportunity to play. I just don't ever want to forget today."

Will Dunlap now turn pro?

"Oh, boy," he replied with a smile when asked whether he had yet considered his playing status going forward.

"I have no idea, I really don't. It's really cool to have that opportunity in the first place and starting the week if you had said 'hey, in five days you're going to have a PGA Tour card or an opportunity for two years' I'd have looked at you sideways.

"But that's something that doesn't just affect me, it affects a lot of people. It's a conversation I need to have with a lot of people before I make that decision."

Dunlap can now take up PGA Tour membership at any point during the remainder of the 2024 season, which would give him exemptions to all this year's Signature Events, the Masters and PGA Championship provided he turned pro before the respective events.

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As the reigning US Amateur champion, Dunlap is currently exempt for the Masters, the US Open and The Open if he retains his current non-pro status.

He has until 30 days after the conclusion of the PGA Tour campaign to take up membership for 2025, otherwise he would have to wait a year to join for 2026.

Irrespective of whether he turns professional between now and then, Dunlap is now able to feature in March's The Players Championship in wake of his victory in California.

He is now also able to play in Full-Field Events through the tournament winners category, up to a maximum of 12.

The PGA Tour now heads to Torrey Pines for the Farmers Insurance Open, with a Wednesday start in San Diego. Watch all four days live on Sky Sports Golf. Stream PGA Tour golf and more on NOW