Itachi utilized his chakra perfectly to outlast Sasuke. Sasuke was being reckless, and constantly was on the defensive using massive chakra portions.
Sasuke only uses one chakra taxing jutsu which was that rebirth jutsu or whatever.
Itachi spammed Amaterasu and used Tsukuyomi, Susano'o, and some Katon and average genjutsu.
Sasuke had zero chakra left when he used Kirin. It was stated he didn't need it to use it.