Ok here is what I think (again).
Of course Nagato is stronger, but Itachi has a chance and he has the means to defeat Nagato. You cannot say Itachi's intelligence cant make up for the gap between their powers, because we cannot decide it unless we see this match .
So I think if Itachi makes the first move and places Nagato under genjutsu,Itachi wins (as for breaking genjutsu,those saying Sasuke 3tomoe sharingan broke tsukuyomi,are wrong!: Itachi didnt want to kill sasuke, he let him break it) .
Now lets say Itachi doesnt use genjutsu on Nagato immediately,or nagato closes his eyes from the start and summons those animals..Itachi easily burns them with amaterasu. Shinra tensei can be withstood,and a person cannot be pulled out of susanoo that easily . Gedo mazo can be killed with totsuka sword (Im not sure though about it, i may be wrong but still gedo mazo has no effect because of yata mirror). Asura path has no effect because of yata mirror. So lets see CT. It can be cancelled if the black orb is destroyed,. That can be done if Itachi spams yasaka magatama against it IMO but even if not CT needs a few seconds while it pulls Itachi in and Itachi has time to cast one genjutsu. Even if not, he can use izanagi and while izanagi is active all Nagato's attacks are useless and Itachi can cast his genjutsu even if losing his eye. So Itachi can win but I dont say it would happen as I wrote.