Yawn Naruto sucks, but I will partake in this little thread. Itachi is stronger than Sasuke(Itachi is the ONLY character I liked in the manga).
Itachi was ridden with disease, meaning that he couldn't fight at his full strength.
He also never wanted to win that fight, it was always his plan to lose, meaning that he didn't necessarily try to win, he only fought to make it believable.
Etc, etc.