In fighting such a good fight against mayweather. Some thought he even won the first fight.. May has just looked unstoppable through out his whole career.
Mayweather fought with one arm that fight, FFS. We know what happened the second time around when it got healed.
it is not the only time May has fought with one arm. Im not downplaying May, im more surprised that one of the least "known" opponents or hyped, I gues I can say, gave him that good of a fight.
Basically, in the long list of more or less, hyped opponents, castillo of all of them gave him his toughest test
Well in this case, there is proof, when mayweather winning easy against castillo, at the end of the 4th he complained about his shoulder. He tore his rotator cuff, but didnt quit and had a tough opponent in front of him. the second fight, a healthy mayweather outclassed him, although castillo had his moments.
I think Castillo did so well in the first fight for the same reason it took Mayweather 10 rounds to dispose of Ricky Hatton (while it only took Manny only 2 rounds to flatten Hatton).