First thought is WB - Pettis but on a second thought, objectively it has to be lil bro-Guchi
a) Guchi is a better pound for pound fighter than WB and just as good at striking if not better, but much more well rounded
b) Guchi was wiping the floor with Pettis for three rounds, whereas WB may have been winning, but Pettis was hanging in there and he came prepared. Sergio looked completely outclassed, and looked as bad as anyone has in a world title fight.
c) It was for the world title fight won in a championship round over a real world champ in that weight class, validating his previous win.
d) Anthony is a finisher. Sergio is not, which made that even more unlikely.
e) It's a better ko.