Has a fighter ever lost the 'formality' rematch or career defining win?

[match]

As for a past his prime fighter stopping a rising star the only thing that comes to mind is Foreman over Moorer. As for your first example, I'm not sure if this fits because I can't quite remember the odds, but I'm pretty sure Julian Jackson was favored to beat Gerald McClellan the FIRST time they fought, but not sure if he was the favorite or underdog in the rematch (which he got torched in like less than 90 seconds). I do know Evander was a huge underdog in the Tyson rematch and probably would have gone on to stop him in less than 7 rounds.