Lotsa great examples in this thread, but I don't think Ali vs Stevenson is one of them. Ali was a 15 round pro fighter, Stevenson was a 3 round amateur fighter. It was a novelty fight more than a great fight. Kinda like Patterson vs Rademacher (although if memory serves me correctly that was an entertaining fight, but it was still a novelty fight more than anything else).
Morales offered the fight. Nacho/jmm turned it down.
So morales fought pacquiao. And both made a ton of money. Jmm then lost to Chris John in Indonesia for peanuts.
Marquez was gunning for a Pac-Man rematch at the time, where he was expecting a career payday and a win. When it didn't come he decided to say screw the politics. I thought he won against John but it wasn't a robbery like people say. Pretty sure he took something around like 30K for that Indonesia fight. Crazy stuff.
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