Originally posted by: Mongoose
Which doesn't change the fact that Itachi did run away (this is spoilers for 85, btw); Kisame just didn't know why. Looked to me like he spent a lot of his chakra dropping Sasuke with his mind trick and using the black fire to bust out of Frog City; with no Sharingan (notice the eyes fading), he wasn't in any condition to fight the old man, stronger or not.
it is clearly explained that itachi retreated because they were not in a hurry to capture naruto. duh. and of course itachi isn't gonna fight jiraiya after being worn out. jiraiya isn't just an old man, he is one of the sannin after all.