Sasuke beat Itachi(Not Itachi With Killing Intent). Sasuke wasn't winning a necessarily fair fight since Itachi wasn't trying to killl him but neither was Naruto's win of Kurama because his mommy Kushina helped him get the win.
Oh and Sasuke did on several occasions FORCE Itachi to use MS like this one for instance:
CQC was Equal while Sasuke had his sword
Kirin forced Susanoo use
The fact of the matter is Itachi may have lost and he may have been sick but he needed to use MS techniques which were a big drain on him. EMS is the transplanting of eyes, Sasuke's goal in life was killing Itachi and he did it at the end of the day he was standing and Itachi was dead.
Oh and Sasuke did on several occasions FORCE Itachi to use MS like this one for instance:
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CQC was Equal while Sasuke had his sword
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Kirin forced Susanoo use
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The fact of the matter is Itachi may have lost and he may have been sick but he needed to use MS techniques which were a big drain on him. EMS is the transplanting of eyes, Sasuke's goal in life was killing Itachi and he did it at the end of the day he was standing and Itachi was dead.