This would not even be a close battle. Pain is the most powerful ninja we have seen thus far in the manga. One may say that naruto is more powerful because he technically "won," but then you must take into consideration how exactly he did that.
When they engaged, Pain had already killed multiple high level ninjas and had leveled the whole of Konoha(most powerful hidden village in the manga) by himself. A single ninja did the work of an army, a power that has never been glimpsed since or before. Can we begin to imagine what he would have done in a full 1v1 battle had he not just used that much chakra?
You must also remember that in his fight versus naruto, Deva path, the most powerful path, was MIA because he had just crushed half of the village in one jutsu. Thus pain was not able to form his usual strategy against naruto and was much weaker than he would be in a true 1v1 engagement. Even so, you must rememeber that he had naruto dead to rights and was he not forced to bring the host back alive, could have ended it with a chakra rod to the skull while naruto was pinned and helpless. I assume against sasuke, pain would have no reason to take him alive? Therefore allowing him to fight full boar.
We cannot imagine what Pain could have done had he been at full power and not been trying to avoid dealing a killing blow to naruto. Considering he is the same ninja who leveled a village, fought off an eight tailed beast, killed hanzo(who defeated all 3 sannin at once), and oh yes, brought a whole village back to life; I think it is safe to say he would have put our favorite protagonist into a pile of dust.
This is a silly argument because it stems from the idea that Pain was defeated by another ninja. Pain was never defeated by a ninja, Pain was defeated by an entire village and most likely he was even then only defeated because he was not allowed to simply kill the most powerful member of that village when he easily could have.
Pain at full power vs sasuke would be, a bad joke. These two ninja are not on the same level, and until we see some special out of madara, it is safe to say that Pain is leaps and bounds more powerful than any ninja yet seen in the manga.
*As a side note: You are also forgetting some very simple strategy. Sasuke is a genjutsu reliant ninja, Pain has eyes that are more powerful than even the sharingan. He has only ever been caught in one genjutsu, and notice right away that that genjutsu was one that had to be delivered through the ears and not the eyes. It is safe to say that pulling off an eye tech against the most powerful eyes in the manga would be nearly impossible. Also note that the advice given to naruto when fighting a genjutsu user was "to go get help, you cannot fight them 1v1." Genjutsu users get exponentially weaker vs more opponents. So pain, considering there are six of him in perfect unison; is probably a sharingan users worst nightmare. These facts, ontop of what I already mentioned, just make the battle that much more lopsided.