Last time I checked Tsukuyomi = Genjutsu = Illusion.
Part 1, in order to use Amaterasu, you have to awaken Tsukuyomi, Itachi said it. And in order to have Susano'o you have to have them both.
If he doesn't used it, it doesn't mean he doesn't have it.
Plus, that's not his style. That was more...