You certainly are misinformed, as the following statements prove.
Blaze Release which is even faster [than Amaterasu]
Sasuke can't seriously harm Mizukage with his fire techiques
genjutsu, would be useless in front of a skilled genjutsu user like Mizukage
You're overlooking a
major detail: Nidaime Mizukage uses the same ability as Suigetsu and Mangetsu, but instead of water, he turns into oil; meaning that fire is actually one of his worst nightmares. Gaara first stated that his body's liquid form resembles oil more than it does water when it comes to the consitency, Oonoki confirmed that it's actual oil by explaing Jouki Boy. Your claim that he turns into a mixture of both is a mere assumption, and it was nowhere stated nor implied that he can
choose whether he wants to turn into oil or water. As soon as Sasuke figures the oil out, which shouldn't take too long considering its very consistence and Sasuke's analytical prowess, the Mizukage is a dead man.
You're also wrong about Genjutsu. Being skilled at Genjutsu is not enough to break the Sharingan's hypnotic illusions, especially when they exceed the affection of just the eyes. [
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] Orochimaru and Shee were both extremely skilled in the arts of Genjutsu (with the former having 5 points, the very maximum, at that category), yet they were unable to break the Sharingan's Genjutsu. Just as Itachi and Sasuke are both extraordinary skilled when it comes to Genjutu, yet fell prey to Kabuto's Senjutsu enhanced flute Genjutsu and couldn't break it by normal means. If Sasuke manages to to trap him inside one of his stronger illusions, I don't see him escaping. Mizukage's Genjutsu, on the other hand, is basically useless against Sasuke, as his Sharingan (that demonstrated its capability of breaking visio-affecting Genjutsu more than once) will see right through it, giving the clear edge to Sasuke in that department.
All in all, I see Sasuke winning this match.