I remember that kakashi mentioned in a falshback to Sasuke's training before the Chuunin 3rd round that if he lets the seal take over that he'll never be as strong as Itachi it was like 2 or 3 episodes (anime) ago or something. Unless the cursed seal can be reversed somehow by Jiraiya or Tsunade i don't think Sasuke has a chance of defeating Itachi.