The most dominant performance against an all-time great in his peak was Foreman's obliteration of Frazier in 1973. Granted, Ali was the best of that generation. But Frazier had beaten Ali and was undefeated (as was Foreman). And both fighters were in their red-hot primes. In contrast, PacMan is decidedly past his prime and Mayweaher is at the tail end of it.