Board Thread:Naruto Discussions/@comment-25531508-20140923043228/@comment-1018594-20140924190439

Let's not forget another factor in the Orochimaru fight: Hiruzen was heartbroken, in addition to the shock of having to fight his former masters. He didn't want to fight or kill Orochimaru for the majority of the fight because he was his favorite student.

Just like Kakashi didn't wanna kill Obito when he had multiple chances to, but once he came to the conclusion that he had to it, Kakashi started kicking his ass all over Kamui's dimension. If Hiruzen had the "I don't feel bad about killing you" mentality from the jump, it would have been much easier on him as a battle.