Its very rare that a Heavyweight beats a 'great' in their prime

[KingAL]

How can Ali be past it,when he beats Foreman a year after Frazier beat him?
And how can Frazier be past it when Ali beats him a year after the Frazier fight?

Sorry, say that again

Just edited
If Foreman/Frazier was two greats in their prime
Ali beats Foreman 1 year after Frazier/Ali 1
So Frazier/Ali 1 would logically be two greats in their prime
And if Foreman/Frazier was two greats in their prime
Ali/Frazier 2 happened a year after it

You're confusing me, so let's get the chronology right, guys.
Ali-Frazier 1 - March 1971
Foreman-Frazier 1 - January 1973
Ali-Frazier 2 - January 1974
Ali-Foreman - October 1974 (not 1 year, but 3½ years after Ali-Frazier 1, and also after Ali-Frazier 2 had already taken place)

In Ali-Frazier 1 you had two greats, but only one, Frazier - the winner - in his prime. I think it's fair to describe Foreman-Frazier 1 as two greats in their prime (although it doesn't matter if Foreman wasn't as the requirement is that the loser is a great in their prime). However, some argue that Frazier's win over Ali took more out of the former than the latter, and he was never the same fighter again. Given the style of Foreman's win - a quick blitzing, as Frazier was just made for George - I think it's a moot point whether Frazier was still in his prime. Essentially, Foreman would have beaten a prime or sub-prime Frazier. Regarding Ali-Frazier 2, the question is still whether or not Frazier was prime following both a gruelling battle with Ali 3 years before and a devastating defeat a year earlier against Big George. Ali certainly wasn't prime, despite being the easy winner, but he didn't have to contend with a layoff unlike 3 years earlier (despite his two 1970 warmup fights). Honestly, I simply don't know if Frazier was still prime!

Regarding Ali-Foreman, I think it's safe to argue that Foreman was prime. Ali certainly wasn't, but the winner doesn't have to be, and the victory merely reinforced his own greatness and legend.