If he trained for those circumstances, and slowed his pace to that of Battling Nelson's, then he would last the whole fight just as easily as Nelson. However, that would be irrelevant as Mayweather would more than likely knock him out in a number of rounds.
A real tortoise and hare contest Floyd pitty patting like a machine for 20 rounds Nelson covering up and pressing constantly and fouling when he can. After round 25 the tide turns and Nelson starts to hit Floyd flush. Round 35 Floyd barfs in his corner, Nelson spits out a few teeth. Round 45 movement has ceased, just two guys centre ring punching each other. Nelson takes the decision.
