The fight where Ip Man goes up against ten of the Japanese Karate black belts. This is the first time you see him fighting without concern for the health or safety of the other guy, and holy crap, does it show.
This fight starts off with Ip Man catching a dude out of the air, slamming him on the ground, and stepping directly on his head.
Even better, it was established in an earlier scene with his son that he hasn't been practicing that much since the Japanese takeover. This means that he was essentially 'rusty' (for lack of a better word) during his fight with the ten black belts, and he still kicked their asses like no one's business.
During the final fight in the first movie with General Miura, Ip Man managed to corner his opponent to a pillar. The next scene can be described as the ultimate text book ass kicking, wing chun style, where the flashback scene of Ip training with the wooden dummy is cut in between him going to town with the General's ass. Cue the combo meter racking up really quickly as Ip shows the General what wing chun combos are about.