James Lawton: All champions have to fade sometime, but this pair went out fighting

Kauto Star was the first of the mighty to fall, and with hideous possibilities, and then the other, Denman, was chopped down, blow by pummelling blow up through the cruellest rising ground in racing.

But if it was the end of one of the greatest double acts in the history of racing it was no time for mourning.

Neither Kauto Star nor Denman for a moment breathed the concept of surrender as the new champion, Imperial Commander, relentlessly drove them towards the close of a magnificent era.

The heroes may have been forced from the centre of the stage, but, after all, even the greatest of them have to go sooner or later, and it was not before they reminded us precisely of quite who they were and what they had been.

Indeed, if there was an inevitable sadness in the rain and the mist of the valley, there was also a wonderful sense of deliverance.

It was because the fall of the most beloved of jumpers since the grey Dessie and the most admired after the imperious and untouchable Arkle might well have carried tragedy as well as the heaviest pathos.

A terrible collective groan greeted the potentially catastrophic sight of Kauto Star spilling his rider Ruby Walsh four fences from the finish. It was a crash that conjured again all the concerns for the Kauto Star who in his youth ran like an equine god but often jumped in the fashion of an air-headed adolescent.

The fear of everyone, the most innocent of the crowd and the hard-eyed professionals, was that the superb horse might easily have broken his precariously extended neck.

Instead, there came another great noise, this time a roar of relief, when Walsh clambered back aboard and cantered home with the air of a man who was plainly aware that things could have been so much worse. "There's not a bother on him," Walsh reassured the world.

Last year Kauto Star and Walsh were an unbeatable duo filled with the confidence bestowed by the most superior talent. Yesterday they had to fight to stay with not only their old, hard-punching rival but a new challenger full of both ambition and the stamina he was supposed not to possess.

The great Tony McCoy, aboard Denman for only the second time (the first brought a disaster at Newbury last month) had to fight another kind of battle, a raw, elemental test of strength with Imperial Commander, who is trained literally over the hill from the course which Kauto Star, in 2007 and last year, and Denman in 2008 had staked out as their own.

In McCoy's case the challenge was to punch it out with a dangerous contender and hope that, ultimately, the ferocious battler beneath him could produce the deeper strength.

McCoy realised that he wouldn't know his fate until they hit that rising ground which each year eviscerates so many of the highest hopes. In the meantime, he could only try to squeeze the life out of the field, draw from Denman every morsel of his formidable force.

It is McCoy's style and so often his destiny, but he also knew that Imperial Commander was running a race of brilliant commitment. The issue was both one of heart and working sinew.

For Walsh the problem ran much deeper, and soon enough was proving insurmountable after Kauto Star seemed to have regressed to the worst of his failings, a belief that he could simply run through a fence without any need to jump it. It was the 12th and it was the moment Walsh knew that his chances of winning had just about disappeared. Amazingly, Kauto Star ran on – but not as the same horse who had approached that fateful fence. He was a fighter attempting to clear his head. Unfortunately, on this occasion the challenge was too great.

If you are Ruby Walsh, of course, you are not permitted to abandon the task. You do everything you can to stay in the race. He moved Kauto Star from the inside to out, he once gave it a lash of some intensity, all the time hoping that he could reconjure some of the glory and perfection of last year.

The boxing metaphor endured. Before the race, when the Gold Cup score between Kauto Star and Denman was 1-1 and the billing for the latest collision was The Decider, comparisons between the showdown in Manila between Muhammad Ali and Joe Frazier were maybe inevitable. After the brush with disaster at the 12th, there was no longer a point of relevance. There were now three fighters in the ring, Denman, Imperial Commmander and Kauto Star.

"We were in trouble after the first mistake," said Walsh. "The job was to hang in and hope that the horse would get something back." Later the verdict on Kauto Star was quite harsh. It said that like a fighter who had suddenly hit the notorious "wall", Kauto was suddenly bereft of all the best of his talent. You wouldn't have thought so in the early going.

Kauto Star was moving then with all of the old snap and beauty. Denman pounded forward. History was grouping itself around two great horses once again. However, Paddy Brennan aboard Imperial Commander also had his part to play. He was, he said, reaching out for the "greatest day of my life."

It meant that belief in the old order, an inevitable duel at the finish between the horses that had annexed jump racing's great prize, was, stride by stride, stripped away.

There was another consequence of historical weight. In some eyes Kauto Star was running for more than a third Gold Cup here. He was contending for a place alongside Arkle, not only in the number of his Gold Cup triumphs but in the definition of his greatness. This, when you looked at the detail of Arkle, the extraordinary nature of his talent and character and the mockery he made of the harshest handicapping, was always an idea hinting at the power of modern fantasy, and perhaps also some of its hype.

In the end though there was a conclusion that dwarfed all such arguments. It was that two brave and brilliant horses had galloped off, possibly for the last time, with their limbs sound and nothing less than their honour again lighting up the valley – the one where they will surely never be forgotten.