Itachi didn't "beat" Nagato. Itachi Orochimaru'd Nagato. He off-paneled the summons' eyes and Nagato's arm. And then skewered Nagato like a shish kebab in between panels after saving Naruto and Bee.
HOWEVER, I am fully aware that there were mitigating circumstances, and that it wasn't a true and replicable victory, but still, I cannot pancake believe Nagato fans are still insisting Nagato's in a different tier altogether.
Especially when they ignore opposing mitigating circumstances, like an immediate Chibaku Tensei, Itachi's obligation to save Naruto and Bee, Nagato being sucked up in his own Chibaku Tensei, etc.
Plot no Jutsu works both ways, and people are ignoring that when convenient. Nagato was freaking armless and without summons while two living blitz-kings, Itachi and Naruto, were chatting.