Every recorded result
shownNaruto · ch. 146–147Upset
Itachi Uchiha beat Sasuke Uchiha in Naruto.
Sasuke is left broken under Tsukuyomi; Itachi then withdraws from Jiraiya, not from him.
shownNaruto · ch. 393–394Confirms the ladder
Sasuke Uchiha beat Itachi Uchiha in Naruto.
Itachi collapses from his illness and dies at the end of it. Zetsu remarks that he fought below his strength, and a later chapter says Itachi orchestrated his own death.
What each of them is ranked on
1 win · Sasuke Uchiha · rank 6
shippuden
The other half of every fight in the tier above him, and the half that brings the tools rather than the volume — the Rinnegan lets him move between the same dimensions Kaguya uses to escape, which is what turns those fights from unwinnable into merely desperate. Carries the identical paperwork problem to Naruto: never promoted past the entry grade, having left the village before any retest could happen.
shownNaruto · Fourth Shinobi World War arc
Fights Madara with the Rinnegan and a complete Susanoo. — 2014
shownBoruto: Naruto Next Generations · Momoshiki arc
Fights Momoshiki alongside Naruto. — 2016
1 win · Itachi Uchiha · rank 8
classic · shippuden
Joint holder of the largest figure the books ever issued, and he does not survive to meet anything in the tier above him. The record supports the number as far as it goes — a complete Susanoo, a genjutsu nobody counters honestly, and a fight against his own brother that he loses on purpose while dying of an illness. What it cannot do is compare him to opponents who arrived after the book went to print.
statedNaruto Databook 3 · 2008
Rated 35.5 of a possible 40, the joint highest total published.
shownNaruto · Sasuke and Itachi arc
Fights Sasuke using Susanoo and dies at the end of the encounter. — 2008
What this does not settle
2 results, each cited, and the tally counts every one of them the same. That is its rough edge: a win at one side's lowest weighs as much as a win at its peak, which is why a level score goes to the latest result rather than to a judgement about which fight mattered. It is a record of meetings, not a ranking of its own.
The ladder above it is argued from everything either of them has been shown doing; this page is argued from these 2 citations.
Where the two disagree, the disagreement is the point, and it stays visible rather than being resolved by whichever of them happens to be on this page.