It was, of course, Tiger Woods — a softer, more agreeable version, perhaps, but still a superb example of what can happen when wholly original talent is shaped by a most formidable will.
Yet if the linking of the achievements of a 21-year-old Woods, who ransacked the 1997 US Masters and the record-shattering mark established by McIlroy at 22, in the most challenging of the majors, the US Open, at the Congressional Country Club, creates the possibility of one of sport's great dramas over the next few years, for some there must be another comparison running back much further in the sports blood of Northern Ireland.
For some, at least, McIlroy's stupendous feat in Maryland was a sublime provocation to journey back to the Estadio da Luz in Lisbon on the occasion of George Best's first assault on the consciousness of the world.
Back then, in 1966, Best was still in some ways like his compatriot McIlroy. He was largely innocent of the ways of the world.
He lived in a council house in Chorlton-cum-Hardy and his first lunges at the dawning celebrity culture were so naive that today they would have inspired a massive cringe amid the occupants of the fast lane.
McIlroy, supported by his family and such a warm, knowing friend as Graeme McDowell, the reigning US Open champion he so spectacularly usurped, is at the shortest odds to avoid the pitfalls of the essentially shy, handsome youth who returned from Lisbon wearing a sombrero and a label denoted by the Portuguese media — O Quinto Beatle — the Fifth Beatle.
However, for a little while at the weekend, they were inextricably linked in the minds of anyone who remembered the Best outpouring and saw in McIlroy's easy domination of all his rivals the same level of exuberant discovery that for a little while at least he was quite unmatchable by anyone who stood in his way.
Manchester United manager Sir Matt Busby advised caution in the away leg of the European Cup quarter-final against Benfica.
“Feel your way into the game,” were the instructions from the Scot.
“This is a brilliant, dangerous team and if we get carried away early, they will punish us for sure.”
Best may or may not have been listening.
In any case, that night he was about as cautious as a hungry wolverine.
From the first whistle, he ran at Benfica with almost abandoned relish.
He scored two goals and caused panic whenever he had the ball at his feet. United scored five and moved serenely into the semi-finals of the competition.
In the dressing room, midfielder Pat Crerand said with heavy irony: “Isn't it a good job the kid listened to the Old Man?”
At Bethesda there could only be rejoicing that, 45 years after Best's supreme performance, Rory McIlroy was also so attuned to the inner voice which persuaded him that it was time to respond to all the promptings of his extraordinary talent to hit the golf ball with an ease that was so natural, so withering of all opponents, that some believed — a little unrealistically — that he would now be able to reproduce the scale of it whenever he walks on to a course.
It is, you have to believe, indeed a fanciful idea, but it does nothing to relegate the significance of what he achieved over the last days — and that for as long as he plays golf he will create the possibilities of thrilling experience for all who watch him.
Translating this swiftly into a sure-fire challenge, not only to the Tiger's 14 majors, but the 18 of Jack Nicklaus is, plainly, a huge reach.
It is to presume that McIlroy will sail serenely through the rest of his career, that the kind of pressures which gave a player as distinguished as Tom Watson the yips will never again touch the boy who died at Augusta and was resurrected in Bethesda.
It presumes that none of his rivals will ever feel the release and the magic of absolute confidence that came to him when he began to dismantle the US Open records or that there will not be some new young rivals even now dedicating themselves to the highest challenges of the sport. There is another hasty projection. It is that at the age of 35 the time of the Tiger is over — that he will now always be marooned in his angst and his exhausted haul of majors.
It is a simplicity that maybe too readily dismisses the achievements of the man whose life crashed down so vertiginously when he drove into a fire hydrant.
Woods has been chastised for a tardy reaction to McIlroy's sensational eruption, but this is not something he is likely to dwell upon for too long.
Not all of his memories of his own dramatic emergence are of the warmest variety.
There were resentment and scepticism and soon enough he was obliged to apply the force, not of his anger, but the range of his talent and the intensity of his focus.
Woods knows, better than anyone, the pressures that his young rival has drawn to himself.
Certainly, there is the possibility that the brilliance of McIlroy may provoke in Woods a new resolve to claim back at least some of his empire. If it is so, it is not the least of the young man's gift to golf.
The ultimate one, though, is the one he shares with his tragic countryman George Best.
It is to remind us of what can happen when a young sportsman refuses to believe that there is nothing he cannot achieve.
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