A couple:
Marvin Hagler Vs. Tommy Hearns. Hearns came out flying and cut Hagler early in the first round. Hagler managed to take over from there and proceeded to beat Hearns to a pulp.
My favorite was because I was there:
Lyndon Byers v. Wayne Van Dorp Boston Garden. Byers had beaten up Van Dorp twice already. In the 3rd period, at the face off circle, Van Dorp was jawing and smacking Byers stick but the commercial light was on. Byers just stared at the commercial light he was not going to waste this during a TV timeout.
As soon as the light went off, Byers dropped the gloves and his stick in one motion and hit Van Dorp square in the nose. Van Dorp just crumbled to the ice. Van Dorp refused to step back out onto the ice because the Boston Garden fans were just going nuts.
I saw the Hearns-Hagler fight on closed circuit at a theatre in New Bedford. Probably the best early round fight ever fought.