Why did Bernard Hopkins have so much trouble w/Segundo Mercado?

Why did Bernard Hopkins have so much trouble in the first meeting against Segundo Mercado? Hopkins aggression in many rounds seemed ineffective as he was taking many counter shots. I think if he wasn't so incredibly conditioned, he def. would have lost this fight, though it could be argued whether or not Mercado deserved the nod. What do you cats here think? I have this fight somewhere and although I hate to make an excuse for Bernard I know he traveled to Columbia, I think to make this fight. He seemed very not himself that night and I think Mercado fought the fight of his life. Mercado was a very big dude and awkward. Outside of that Hopkins just fought like shit, it happens.