OP: It's true that Itachi is a master of genjutsu, but Obito is very proficient with that as well - do you really think he would be caught in a genjutsu which would allow Itachi to control Obito? As a testament to Obito's proficiency with genjutsu, he was able to take control of Kurama, a feat only accomplished by Madara besides him. In fact, Obito presented a genjutsu controlling the opponent when he fought Konan - and he utilized this genjutsu in the middle of a fight. Itachi's only use of such genjutsu was on immobilized Kabuto under Izanami. So basically no, Itachi won't make Obito tangible by controlling him.
Susanoo won't give Itachi much, because Obito can simply slip through it with Kamui and lay his hands on Itachi then.
However, an even stronger argument against Susanoo is that Itachi cannot maintain it for long - it drains his chakra horribly. In other words, Susanoo is useful for him only if he can finish his opponent fast with it and unfortunately, Obito can prolong the fight almost as much as he likes. He can just turn intangible and drink some afternoon tea while Itachi knocks himself out by using Susanoo.
Obito's only real danger is Tsukyomi, but - because of the fact he can turn intangible, he can avoid eye contact without any risk.
And how Obito can defeat Itachi? Simply by touching him. Even Minato, who's much faster than Itachi, barely managed to get away from Obito's Kamui and Obito himself stated he can use it faster and that "next time he will warp Minato as soon as he touches him".
As you can see, Obito wins this rather easily, with the use of one jutsu only. Now remember that he has many more in his arsenal.
So, to sum it up:
-Because of his low stamina, Itachi's best bet at fighting is defeating his opponent as soon as possible. Unfortunately, Obito can prolong the fight as much as he wants.
-Susanoo is useless because of the reason stated above.
-Amaterasu is useless because of Obito's kamui.
-Tsukyomi is Itachi's only chance of winning, but Obito can avoid it relatively easily as well, because he can focus entirely on it (all of Itachi's other techniques present no risk to Obito)