The fight is a complete crapshoot unfortunately. Its probably one of the few instances in Dark Souls I would call grossly unfair, and every reviewer who does a long form review of the game will generally point it out as such.Fucking hell. I thought he wasn't supposed to attack until you got to the middle of the room... How the hell do you get past him to the stairs?
Edit: oh, random chance is the answer I see... Guess I'll keep trying.