Amaterasu is no problem as long it doesn´t hit Luffy. People like Ay dodge it without trouble, so will Luffy.
Plus, he can´t even suprised by it, because his Precognition. The only problem that exist would be Gen-Jutsu and if Itachi activates his Susanoo. I would say, as long the battle appeared in charcter, Itachi uses the old fashioned way and Gen-Jutsu GG.