Sasuke performed remarkably well against Itachi (although Itachi was eventually revealed to be dying) until the latter unleashed his Susanoo, equipped with the Yata Mirror and the Totsuka Blade.
A matchup between Eternal Mangekyou Sharingan (EMS) Sasuke and Itachi is debatable otherwise, as EMS Sasuke has access to a version of Susanoo that carries no visible side effects for the user, unlike the regular Susanoo that served as the catalyst for Itachi's death.