Clearly when he fought Sasuke when he was alive because that was when he revealed all of his powers like Amaterasu, Tsukyomi and Susano except for Izanami of course, maybe he couldn't use it then due to lack of Senju DNA, please see this for more info >
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. Although, that time may not count because Itachi is supposed to have not been trying to intentionally defeat Sasuke.
