I agree with Kraco, Zaraki was bored when he faught Ichigo. He wanted to have some fun. He was just caught by surprise that Ichigo could release that much power. But unless Zaraki underestimates someone who has a #5 on his tongue and believes that these Espadas (who would need to have NEVER shown any HUGE skills in order to be similar to the Ichigo vs. Kenpachi fight) are somehow weaker than Zaraki expects them to be... in the middle of Los Noches... well he'd have to be incredibly stupid.

I always got the impression that the only reason Ichigo won against Zaraki is because Zaraki got caught by surprise. But if it wasn't for that, I think it would have been different.