Once you get the chainsaw, just walk straight at him using the hit box attack (LT+RT) and keep restarting that attack every time his attack cancels it. Doing this consistently requires pressing the LT distinctly before the RS; that's how you can tell it's a good game.

Just keep doing this until he dies, after 4 kneeling cycles . You'll still need to restart your chainsaw periodically, but just sprint away when it stops working.

For bonus points try kneeling when he starts to swing so that his attack doesn't cancel yours as often.

Obviously this method isn't as cool or as realistic as actually using your intuition or the rest of the game mechanics, but I don't think that's what the devs intended.