Getting the body shot when he comes in for the piston punch is the easiest way to KO him. If he doesn't go down, or you miss, you can also get a ton of stars on him throughout the fight just by punching him. When he's standing there, before he twitches his eyebrows, just punch him in the face. He'll block two for every one you land (so you'll eat up your hearts pretty quickly), but most of the shots you land should give you stars. Then, just dodge, stun and unload.
Just practice dodging the punches. If you can dodge and get back in more quickly then you can score more hits on him and beat him faster.
He can be a bit tough to take down in the first round, so what you should try is to get his energy really low and then keep it there until the end of the first round. That way it'll be easier to get a TKO in round 2.
ITT: people who think westernized names are standard. - Kabuki Tanooki I live in the East coast and I hear all this crap - Audiosol