1. maybe it's just a clone, and the real naruto will be somehwere else
2. maybe there's a shadow clone gathering natural energy, and suddenly naruto turns into sm and counters it.
3. maybe sakura or kakashi suddenly come to le rescue
4. maybe something will happen to sasuke so he can't proceed (like huge pain in arm or something, or still not enough chakra)
5. maybe naruto still has the energy to dodge/counter
dunno .-.