You already lost by sentence one. Itachi has the fastest seal speed in the manga; faster than even the Sharingan can keep track of. By the time Minato can make even a single shadow clone, Itachi has already made the seals and cast his Finger Genjutsu.
Literally Minato's only chance is to try a Shunshin blitz, but seeing as how Itachi can activate Susano'o in 1/1000th of a second, that's not going to work either.
Minato's arsenal can win against Itachi, but only if he can win turn 1. And he can never win turn 1.
That's how Itachi loses.
Minato will push him further until he tires with using Susanoo, while Itachi can't put pressure on Minato since he practically can slip out of anything Itachi throws at him.
Realizing he's encapsulated by genutsu prowess is all it takes for Minato to escape. And we've already went over how Minato is an excellent sensor-type (he could simply place his finger on the ground and deduce how many shinobi there were within his vicinity)
So I can actually see Minato detecting every time he's placed under genjutsu and teleporting away causing a disturbance in Itachi's control which is the formula for genjutsu.
And yeah, Minato doesn't have many chances, but so does Itachi. Both are formidable opponents that are famous for exploiting weaknesses, but it comes down to durability and how much intel the other can gather to exploit.
I can also see Itachi winning, but his chance is Tsukuyomi, and tricking Minato in the coordination of his kunai. But he can't damage him with ninjutsu or taijutsu alone and that's where Minato pops up.
But it'd be an epic fight to watch.