Maidana had Floyd on the ropes a lot in the early rounds but if you look closely nothing really landed. Marcos got him with one of those overhand rights early (which didn't seem to affect Floyd) and he kept trying that over and over and over again. As the fight went on Floyd figured out Maidana's attempt with that wild overhand right, and dodged it everytime.
It wasn't Floyd's best performance and he knew it by the disappointing look on his face post fight, but he definitely won. Marcos is a brawler and him always coming forward made him look like the aggressor, but Floyd landed the better punches
EDIT: amen Kola Nuts, glad someone saw the same fight as me