Khan's dodgy chin was shown for all to see in a few fights before that. And that fight shows all it was was a punchers chance win. Look at how their careers have differed since the fight.
Prescott? My vote goes to Weaver/Tate though I'm not sure it was an upset. Great comeback ko that's worth rewatching from me. Also, Taylor-Chavez assuming Chavez was the underdog. I think he was but I could be wrong:think.