I would assume the top 5 genin (pre-shippuden) would be Neji, Naruto, Sasuke, Gaara, and quite possibly Shikamaru. This is a, somewhat, nice team, but what exactly are they going to do against Itachi's susanoo, tsukuyomi, and other op techniques?
None of their attacks are able to pierce susanoo, only option would be for Gaara to pull him out, therefore cast tsukuyomi on him and destroy the rest of them.
Tsukuyomi, as it is, is able to break down the opponents psyche and assuming he can use it repeatedly like he did against Sasuke, he should have a few shots off on the others.
Amaterasu? Only thing that (I believe) could possibly stop it would be Gaara's sand but even that isn't fast enough to shield absolutely everyone in time.
So yeah, I can't exactly see them defeating Itachi in this case. I'm willing to be proven wrong though.