Two weeks ago, Golf Australia Express predicted the young Spaniard would breakthrough for his first PGA Tour victory in 2017. But not even the experts could have predicted that storyline would come true so quickly and against such an impressive field.

Eight months ago, Rahm was 551st in the world ranking. Now he’s destined to storm into the top-100. And he did it in style.

Less than 48 hours earlier, the event took a massive hit with its biggest stars all checking out after 36 holes. Tiger Woods, World No.1 Jason Day, reigning US Open champ Dustin Johnson, PGA champ Jimmy Walker and Rickie Fowler all missed the cut at Torrey Pines.

But in the heat of the action on Sunday afternoon, the stars had almost been forgotten as a clogged leaderboard kept the galleries in full voice. A cavalcade of players had their chance to win as one after another grabbed a share of the lead. At one stage, nine players were atop the leaderboard and another 20-odd within striking distance.

The ball-striking was superb and some hearts were broken. Victorian Marc Leishman had a share of the lead early in the final round but a double bogey at the par-4 7th hole halted his run.

But it was Rahm who grabbed his opportunity with both hands as he rattled home in a six under 30 on the back nine to win his maiden PGA Tour title by three strokes.

The 22-year-old started the day poorly with a three-putt bogey at the par-4 1st hole but he grabbed two birdies at the 3rd and 5th holes to get back into the red.

The real fireworks began at the par-3 11th when Rahm rolled in a 13-footer for his third birdie of the day. Two holes later, he reached the par-5 in two shots and converted the eagle putt from 18 feet to move to 10 under and a share of the lead.

Rahm’s best was yet to come. At the long par-4 17th, his approach finished close and he rolled in the birdie. On the par-5 18th, he played conservatively by firing his second shot long the flag, which was nestled just beyond the deep pond fronting the green. He was left with a 60-foot downhill putt for eagle, which trickled down the slope and dropped in the cup at the perfect speed. With several groups still out on the course, Rahm was in the house with a seven under 65 and unbeatable at 13 under as sat three strokes clear of the field.

Jon Rahm rips his drive off the 18th tee during the final round. PHOTO: Donald Mirelle/Getty Images.

Charles Howell III (68) and C.T. Pan (70) finished tied second at 10 under. Four players, including major champions Justin Rose (70) and Keegan Bradley (67) finished a further shot back in equal fourth at nine under.

FINAL LEADERBOARD

Rahm joins Gary Player, Jose Maria Olazabal and Jason Day as the only international players to win at this Torrey Pines tournament since it began in 1952.

“It was important to keep composure, keep it going and I'm just so glad I was able to keep my mind on the game and I was able to think clearly and I'm just so happy it finally happened,” Rahm said.

“My heart was beating so fast that I just couldn't think,” he said of the closing putt.

“What I wanted to do, I was aiming about three feet left of the pin, maybe a little more, to a little spike mark that was there and I was trying to just get it there. That was my goal. Start it on that line and get it to that line.

“After that, I knew the slope was going to take care of the rest. At first it started breaking right. It kept breaking right and I was just waiting for that ball to come back to the left. At one point I thought it was going to be about a foot short, but it just kept going and it kept going. Then towards the end, it moved a little right and it came back, came back to the left and next thing I know the ball is just coming in, going into the hole.

“It was almost a little bit up to luck, right, just hoping to be lucky, just trying to hit my spot. I did everything I had under my possible control, which was the line and speed.”

The key to this victory was Rahm’s aggressive game plan down the stretch. He says it’s a “Spanish” thing.

“Believe it or not, I was more aggressive when I came to college than I am right now,” he smiled. “I believe it's a Spanish mindset. I feel like we are all pretty aggressive, right? Jose, Seve, Sergio, Alvaro Quiros, people like Jimenez. I feel like we've all been pretty aggressive, I think that's the mindset probably thanks to Seve.

“Yeah, my idol's always been Seve. Obviously I grew up on Tiger and Phil, respecting and admiring both players for what they've done, but my idol, it's always been Seve.

“I try to emulate what he inspired on the golf course. Not play like him because it's a little different to the way I like to play, but try to inspire and express the same emotions he used to.”

Having grabbed a share of the lead early, Leishman made two late bogies to fall back to six under and into a tie for 20th place. Cameron Smith was the next best Australian at four under and tied 33rd.