Greatest combat sport underdogs to pull an upset?

I know it's not technically an upset since Wepner didn't win but nobody thought he'd make it 15 rounds with Ali.

So I'll start with Chuck Wepner.

Buster Douglas.

@comicstooge: I bet you'd know this. I can't remember the name of that dude who wrapped his hands in hard plaster casts & removed the padding from his gloves & still couldn't knock that one dude out.

Antonio Margarito vs Cotto?

@comicstooge: No I found it, it was Luis Resto vs. Billy Collins

Chris Wiedman when he beat Anderson Silva and ended the Streak.

Matt Serra when he beat GSP

Holly Holm when she beat Rousey

Frankie Edgar when he beat BJ Penn the first time

TJ Dillashaw when he punched Renan Barao in the face 800 times

Muhammad Ali (then Cassius Clay) when he was a 8-1 underdog against Sonny Liston

Buster Douglas against Tyson

Michael Bisping when he KO'd Rockhold in the first round.

Gonzanga when he head-kicked Cro-Cop (A lot of people forget about this)

Randleman when he KO'd Cro-Cop (Poor Mirko)

Sokoudju when he KO'd Little Nog

Couture against Belfort