I don't think tsukiyomi is breakable... i think itachi knew sasuke had potential and allowed him to "break it".
Well Itachi stated that it was breakable by someone with the same blood, but Itachi had planned out that HE WAS GOING TO DIE in that fight. This means that he knew tsukuyomi wouldn't finish him off, because that would mean victory for Itachi. All I am saying is that it is completely possible for it to have been broken by Itachi and not Sasuke, considering Itachi's plan accounted for Tsukuyomi failing in any circumstance Sasuke survives the fight with Itachi and Itachi dying.
There are just several things wrong with that tsukuyomi:
Extremely weak in comparison to the tsukuyomi used on Kakashi. Itachi can control the entire world in tsukuyomi and the victim isn't really free to do anything. Itachi could have just started stabbing him instantly, and he likely couldn't focus enough to break out of it.
Would have one shot Sasuke if it had finished, something Itachi didn't want and couldn't allow (since he wanted Sasuke to win). Because of this It could mean that Itachi made his tsukuyomi easier to break out of, or actually broke it himself on purpose (and made Sasuke think he broke it).
edit: The people above me who say he broke it. I understand what the story shows. You have to learn to read underneath. We know that everything about that battle was planned out by Itachi. Itachi couldn't let the tsukuyomi finish off Sasuke or else he would win the fight, which wasn't Itachi's plan. All I am saying is that it is possible the Tsukuyomi was weaker than it should be, broken by Itachi, or Itachi let Sasuke break it. It is completely possible that Itachi had planned for Sasuke to break it as well. I just look at the possibilities, and with a genius such as Itachi any of them is possible.