July 19, 2007, Carnoustie, first round of The Open Championship. An 18-year-old amateur stands on the 18th tee needing a four to shoot 68. There is a little wind in his face, out of bounds down the left, bunkers on the right, the Barry Burn meanders across the fairway but he is young and innocent and cracks his drive gun-barrel straight and long. Beautiful.

He’s now got 230 yards to the flagstick, wind still in his face, greenside trap on the right, out of bounds on the left.

In the mind’s vault, this picture is framed. Rory McIlroy has just hit a two iron, his body has pivoted and settled into the classical finish position, the ball is rising slowly, cutting through the air like a laser, on a perfectly straight line towards the clock of the Carnoustie Hotel that overlooks the 18th green. It stops 15 feet from the hole and two putts later the kid has his 68. That 230-yard missile was one of the finest shots any of us had seen.

And it changed our perception of McIlroy. He was a kid then, although one with a considerable reputation. It wasn’t simply what he had achieved but how early in his life. First hole in one at age nine, world champion at under-10 and, most astonishingly, he shot 61 in the North of Ireland Amateur Championships at the formidable Royal Portrush when he was just 16. But figures, even the most impressive figures, didn’t prepare you for the thunderous magnificence of that two iron.

Two years have passed. Quickly. We are sitting in a meeting room at the Cameron Hotel on Loch Lomond, where he is playing in the Scottish Open this weekend. “I still remember that shot. It was freezing cold that day, I got back to the house where we were staying, I turned on the television and it was on the highlights. That gave me a kick. But the shot, it was almost ignorance. You know what you are doing but you don’t care and that’s a great way to play,” he says.

McIlroy turned professional two months after that 68 at Carnoustie, earned £162,000 in his first three tournaments, and for the past two years he has been learning the ropes of the professional game. Given the level at which he entered, there was much to lose.

“How is education supposed to make me smarter?” Homer Simpson once asked. “Every time I learn something new, it pushes some old stuff out of my brain.” McIlroy needed to retain the old stuff. “I have always tried to keep it very simple, just hit the ball, not think too much about it and not overcomplicate it. Coming into the big championships, it is more about preparing for the golf course and making sure I am right mentally. I have become more consistent this year and that gives me a lot of confidence. I feel I can get round in a 68 or 69 when I’m not playing my best and I appreciate how fortunate I am to be able to play well most of the time.”

Turnberry will be just his fourth major championship. After finishing 42nd at Carnoustie two years ago, he tied for 20th at this year’s Masters and then performed well at last month’s US Open to finish in a tie for 10th.

Such are the expectations that those performances were hardly noticed, or commented on, even in McIlroy’s own home at Holywood in Co Down. “I’m not one for bringing my golf home with me, though my parents and my girlfriend, Holly, do care a lot. But, actually, it was funny after I got home from the US Open. It was about three or four hours [later], I was unpacking my suitcase, putting clothes into the washing machine and I turned to Holly. ‘You haven’t said well done about finishing 10th at Bethpage’. She said, ‘Do I have to?’ and I said, ‘No, definitely not’.”

He tells this little story with the candour of the innocent, conveying a sense of fleeting disappointment banished by the inner, stronger man. There isn’t much that he holds back. On his website, he writes a diary that reveals much of the minutiae of his young life. He tells how he went with his dad, Gerry, to Birmingham last month and bought the Ferrari he had always wanted to own. Around the same time, he bought an Audi RS 6 and though he didn’t mention the cost, there wouldn’t have been much left from a quarter of a million.

In another entry he tells of attending the Ricky Hatton-Manny Pacquiao fight in Las Vegas, Chelsea’s Joe Cole in the seat alongside him, Mariah Carey, Mark Wahlberg and Denzel Washington two rows in front. “It was,” he wrote, “the best six minutes of live sport that I had ever seen.” There is the story of a pro-am in South Africa where he played with Fabio Capello, whom he found to be good company and who didn’t bristle when McIlroy told him who should be in the England team. “His English,” wrote McIlroy, “is better than his golf.”

When he played the PGA Championship at Wentworth, he stayed in Eddie Jordan’s house adjacent to the fourth green, although he admits it was through his caddie JP Fitzgerald’s friendship with Jordan that they got that. And he writes of the day he and his dad were coming out of a shopping mall in West Palm Beach, Florida, when they saw Jack Nicklaus going to his car. Nicklaus recognised him. “Ah, Rory, how are you?” When Gerry McIlroy said: “Ah, Jack, lovely to meet you,” his son would later correct him. “Dad, it’s Mr Nicklaus.”