The unbelievable may be about happen. The Open Championship has been staged since Queen Victoria was in the middle of her reign and here at Turnberry one man has the chance to make sporting history in a way that would eclipse anything that has happened at any of the previous 137 Opens. In all the years since Willie Park Senior won the first Open in 1860 nothing like this has occurred. Nothing potentially so momentous, so significant, so improbable.

Tom Watson leads by one stroke after 54 holes. Only six other men are under par after 54 rigorous holes on this beautiful and demanding course. Watson has a chance of becoming the oldest winner of a major championship - the oldest by more than a decade, furthermore. If Watson succeeds, surely this would be the greatest feat in golf. It would be one of the greatest achievements in sport, never mind golf.

Think of it. Watson, at 59 and the oldest man in the event, holds back the challenges of 155 younger men to win the game's oldest, and some say its greatest, prize.

Such a performance would surpass the victory in the 1986 Masters by Jack Nicklaus when he was 46. It would exceed Ben Hogan's victory in the 1950 US Open, 16 months after he had nearly been killed in a car accident in Texas. Tiger Woods's acquisition of 14 major championships pale in comparison. Even Woods's 15-stroke victory in the 2000 US Open, an achievement Watson calls the most impressive thing he has ever known in golf, would be a lesser achievement than a man who is two months short of his 60th birthday winning one of the game's four annual major championships.

And of course it might not. The odds are that it won't. Logic suggests that Watson's putter, which has been such a support to him so far this week, may yet buckle on the day when he most needs it to be strong.

Watson holds a slender one-stroke lead over his two nearest challengers. There are 25 more men within six strokes of him.

Can he do it? I hope so. What a story that would be. What an achievement.