Fighters who were never the same after losing once

[Britkid]

Foreman after Ali - did anybody mention that?
Michael Nunn after James Toney.

Foreman looked pretty much back to form in 76, the Young fight was the one that cost him 10 years....

As for Nunn, I would say it was the Barkley fight was the one that began Nunn's fall, although the Toney fight was still an upset.