When Sasuke left Konohagakure, it was more thought out than most people would probably assume. He had considered very carefully where his best chances of seeing Itachi dead lie. That was his goal, after all, to see the bastard dead by the only Uchiha he had left alive. Even if he was technically no longer himself, as long as it was his body yit would be enough.

He had to admit, if only to himself, that he could see how others would think his search for power was blind, Grasping at any that came his way, he shamelessly copies jutsu with his Sharingan and turned them to his advantage. That was what the Sharingan was for after all.

When he was young, when Itachi had killed their family, he had been introduced to another level of the Sharingan, one that has special requirements to gain. The Mangenkyo. Itachi wanted him to have that when the fought; his brother was looking for a challenging fight and nothing more, Sasuke would give Itachi more than that; he would make Itachi regret what he had done a thousand times over.

That wasn't why he was fighting Naruto though; this wasn't about gaining the Mangenkyo right now. He just couldn't continue on his quest for power without first getting past the blonde.

It had come down to this, in Sasuke's mind:

Orochimaru would take over his body, and the battle with Itachi would come. Putting aside that neither would face the other alone in actual combat, in the very least both sets of followers would be fighting with each other, leaving the two to face off.

Itachi had the Sharingan, and at that point so would Orochimaru. While it was true that Itachi had the Mangenkyo and he might not, that was unimportant. Simply having the Sharingan was a defense against the Mangenkyo; it allowed the user a buffer against its effects, and coupled with the strength of the users mind, would allow a person to withstand an attack and keep going.

Also, the amount of chakara needed to use the Mangenkyo was great; while it did make for a formidable weapon to unleash on your opponents, it wasn't something you wanted to use if you didn't have the proper back up and a one hundred percent chance of winning with that move alone. It drained you of you chakara and left you unable to fight, so while your opponent was getting over the mental torture, you were faced with being physically exhausted. And with an opponent like Orochimaru, getting over the Mangenkyo would probably be easy in the fact that he had destroyed countless minds by himself over the years.

When it came to jutsu and taijutsu, that was an even match as well. Both his brother and Orochimaru were considered geniuses since their academy days, and that hadn't chanced since. Orochimaru had dedicated the last fifty something years of his life to learning every jutsu and taijutsu method he could get a hold of, while Itachi had had his Sharingan since he was a child to copy everything it saw. Both knew many of the same techniques, and both knew techniques the other had no clue about, but since both would be wielding a Sharingan they simply hat do copy and counter each move as they saw it coming. Eventually they would run out of tricks to pull on the other and it would be a fair fight in that aspect.

Really, it came down to chakara capacity and cunning. Itachi, while being a genius and a powerful shinobi, had had less than twenty years to build his chakara capacity. Orochimaru, on the other hand, had had over fifty years of building his.

There was also the fact that Orochimaru didn't age, so those fifty some years took no toll on him.

That left it to a battle of wits in the end. What they used to counter an attack with and when, and thinking one hundred moves ahead.

That's why he chose Orochimaru.

Genius against genius it would be, but Orochimaru picked apart people's minds for fun; he dissected your thought patterns and came up with every possible way to use them against you. He noticed the thing the Sharingan wasn't designed to pick up, human nature. Taking every habit, belief, and thought to turn against you, people weren't prepared to fight their own minds.

Itachi was nothing but a cold, calculating killer on the other hand. Looking for the most efficient was to take a person down. That's why he wouldn't stand a chance. He wouldn't be prepared to face the mind so different from his own.

So, as he stares down into the unconscious face of Naruto, Sasuke decides not to kill him. The Mangenkyo was useless to him. Sasuke wasn't going to play Itachi's game any more; no, Itachi was already playing his.