Sasuke did win in his fight against itachi but you guys have to be honesty that itachi did let him win. Zetsu noted at several times that itachi wasn't at his best during the fight. Obito even admitted that itachi plan to lose to sasuke. Also if he really wanted to win he could have saved shisui MS for the sasuke fight instead of giving it to naruto. Not to mention instead of transporting ameterasu into sasuke eye for his final move he could have use his susanno to just seal his soul along with orochimaru.