Charlie/Atom landing a huge leaping punch to Zeus's head. The shot's prominent use in the trailer suggests a keen awareness of how awesome this is.
Heck, the first punch Atom lands on Zeus that staggers him. The entire crowd gives a mass gasp of shock. Not just because Zeus is supposedly this invincible, unstoppable force, but because a robot they never thought had a chance managed to stagger him!
Not to mention Charlie and Atom taunting Zeus back into the rope-a-dope in the final round. Watching that battered little machine invite the King of the Robots to take a few more free shots invoked full-on Rule of Cool.
Max jumping into the ring and interrupting the referee after Atom's defeat of Twin Cities to challenge Zeus to a fight any time, any place, is pretty awesome itself.
Atom fighting all five rounds and knocking Zeus to the ground. Yes, he got up after a few seconds, but not only did he last much longer than anyone, he made the undefeatable fall to the ground. Zeus may have won the match, but Atom won the people.