Fenech vs Nelson I *edit* not sure that Tyson vs Razor was PPV too many years ago and now I am old and tired
I was too young to see it when it happened, but Gomez-Pintor was on the undercard of Hearns-Benitez. It says on boxrec that it was on PPV, Closed Circuit, and HBO. In my lifetime, Gatti-Ruelas on the undercard of Lewis-Golota comes to mind. There's probably others, I can't think of them right now.
Tate/Weaver, mainly because of the shocking outcome ... wow. Never saw a career go from 60 to 0 that fast.
. Gomez~Pintor was not only the best undercard fight I ever saw. It was the second greatest fight period I ever saw following Limon~Chacon4 which happened 8 days later
Matthysse vs Molina on the undercard of Mayweather/Canelo I think it was. Perhaps not the highest level of boxing from a technical standpoint, it was however total war. It got me back into boxing in a big way after a few years of not really following the sport closely.
for pure action the best undercard fight I saw live was Freddie Pentleton KO Darryl Tyson. Vincent Pettway kod Simon Brown in the main event. The worst undercard fight I saw live was David Tua Ko of Ken Lutuska. The main event was Pernell Whitaker v. Buddy McGirt II. These might have been showtime and hbo, not ppv. I cant remember
The best PPV undercard fight I saw on TV was Frankie Randall v. JC Chavez I Hector Camacho v. Felix Trinidad was the main event - and was boring as hell