Ok lets understand something- itachi was a bad ass infact Madara kinda feared him, and honnestly the story did not do much focus on itachi abilitys but if that guy can give Naruto some hidden gift and inplanted his black flames in his kid brothers eyes and was a master of genjutsu he could of did any dam thing with that Sharingan so really he was not fighting at his best itachi was the strongest second to Madara in my opinion at his time and just to make you guys understand something itachi was a Genius Anbu at a early age he master his sharingan too fast not only that if anyone is around the guy just know your in a genjutsu already orchi found out the hard way the point is itachi could have done it if he wanted to that battle was not a battle of ability but more of a battle of pushing his brotherto his limit to get the course seal out
Yeah we're not saying Itachi could never have manipulated them black flames of Amateresu... but in this case the lack of evidence does not go in his favor you know? He could extinguish them probably which we saw in the fight against Sasuke... And with Amateresu practice I'm sure he would have been able to, but let's face it... Amateresu wasn't his favorite, he was more of a Genjutsu user.
Right now the only arguments toward itachi being able to use it is he implemented it in Sasuke (I personnally think like someone said that he only implemented the Tobi trap). Which by the way makes me wonder... If Itachi really did gave sasuke his Amateresu abilities... then why didn't he started the amateresu manipulation sooner? Like against Killer Bee.
Or Itachi is so much better than Sasuke of course he could... (He was better, but facts proove he wasn't as good in the mastery of Amateresu as Sasuke was before he was forgotten in the manga)
Or Itachi was a bad ass omg Anbu chief at 13 (Yes he was but that does mean he could manipulate Amateresu)
Or He completely mastered his MS abilities (We can't say that, he mastered Tsukoyomi, not Amateresu, not in what we've read!)
None of this is very convincing... I am an Itachi fan (not my favorite but quite up there really) but I must admit, just because I'm his fan I can't just say he could do anything... He was bad ass enough as it was no need to give him more credit.