pain's chakra capacity is almost similar to naruto...
in terms of chakra:
naruto >>>>>> sasuke, that's why even now at the 4th shinobi war...kishi made it to the point that naruto will be tired once he meets sasuke...and sasuke's very fresh...at least to give sasuke some handicap since the chakra for a KB mode is almost unlimited...
anyway, back to the topic...where in the battle are you seeing sasuke using amaterasu? during the early stage or late stage? as from what we have seen, he's a skill spammer and that means he will run out of chakra easily and become food...
use amaterasu immediately and you'll loose the battle because you'll not even know if it's a clone or not...
plus sage team have ma and pa's frog song genjutsu which catches up even a rinnegan user...so they will keep both snaketeam busy while ma and pa's frog song genjutsu are taking effect then battle will end