As we all know that kakashi along with Obito was able to unlock his Mangekyo Sharingan before konoha incident,at time when itachi was babysitting sasuke and shishui was not even shown..........so it seems that Obito and Kakashi were the first among [itachi,shishui,and ofcourse sasuke{which is obvious}] to awaken their MS............. and Obito is definetely the boss here.

Sorry if already been posted.thnx............