Horse racing fans are rightly talking about the thrilling duel between Shiskin and Energumene in Ascot's Clarence House Chase at the weekend.

It's not often that a much-touted first meeting between two unbeaten horses lives up to all the hype and serves up such a contest.

Only a length separated Nicky Henderson's home-trained Shiskiin from Willie Mullins' raider from Ireland after a right old battle, which looked for a long way like Emergumene would be just too strong.

It inevitably revived memories of the 1975 King George VI and Queen Elizabeth Diamond Stakes when, over the adjoining stretch of Ascot's flat course, Grundy touched off Bustino after a showdown which has never been surpassed.

The debate is already under way about where Shiskin and Energumene might stand in the history of great two-mile chasers. Sports fans are like that - we love to wonder would he or she have beaten him or her, and would they have been too good for them?

But in sports where the protagonists have to dig so deep that it moves us in a way that other contests never can, you have to ask whether it has left a mark. And if so, how much.

Even Muhammad Ali and Joe Frazier were never the same men after their final savage meeting in Manila.

The same went for lots of other boxers who took each other to the limits of endurable punishment in their first fights, but simply could not do it again when they were asked to face each other a second time.

Racehorses are only human, we sometimes say. Well, of course they're not, but they hurt like us when they stick their necks out the way that Shiskin and Energumene did.

We'll hear soon how well both of them seem to have come out of the Ascot race, and how all is set fair for them to meet again in the Champion Chase at March's Cheltenham Festival.

It's a tantalising prospect. Would it be a surprise if, over the undulating Cotswold course and up that horrible hill which has defeated so many down the years, one of them cries 'Not This Time'?