Sasuke pushed Itachi to bring out his Susano'o. By the time he cast his Tsukuyomi on Sasuke, Itachi had the upper hand by several miles. No doubt about it, but he wasn't expecting Sasuke to break out of his genjutsu so soon. Sasuke did so and nearly killed him with Kirin. At that moment, Itachi was forced to put up Susano'o to defend himself. This is also true.
wtf? what type of blasphemy is this?3tomeo sasuke> 3tomeo itachi? get out of here.
Itachi mastered the sharigan at 8 years old, Please do remember Itachi was trying to go all against sasuke which makes sense he would his his MS techs and he was going blind so why not go out with bang?
Because Itachi was trained by his father as he expected him to lead the clan and join in and add him in the coup. By the time he diverted his attention to Sasuke, the massacre happened. Remember how surprised Fugako was when Sasuke mastered the Katon attack all by himself? You have to consider many factors here.
But yes, 3T Itachi was superior to 3T Sasuke.