It worked for me in many challenge fights. In 3 different fights, I had used my hay-maker to knock down my opponent. My opponent moved in so fast. My hay-maker didn't hit on his punching arm, instead, my hay-maker hit on the back of his head. I still remember that my opponent's body was knocked from straight to horizontal, and then dropped onto the ground. I didn't know my hay-maker could knock my opponent's both feet off the ground.
IMO, the "45 degree downward body rotation hay-maker" is a very powerful tool to have in SD situation. It can be used to "interrupt" all aggressive forward attack. Of course to let your opponent to run into your belly kick can be another good one.
Here is an example. The body rotation can move you to be outside of your opponent's striking path. From that angle changing, you are standing on the side of your opponent, and no longer stand in front of him. This way, your hay-maker can reach to the back of his head.
Example - use hay-maker to interrupt straight punch.