Biggest surprise thrashing by an underdog?

Mayorga - Forrest I and, to a lesser degree II. After beating Mosley twice, Vernon was considered the next big thing in boxing but he went toe to toe with the brawling Mayorga and got KTFO. In the rematch i think he wass still the favorite, but seemed gunshy and dropped a decision, although some saw him winning.

 

Back in the day (1974) when being top 10 ranked meant something heavyweight contender Boone Kirkman (32-2) was knocked out cold by "Memphis" Al Jones (6-21). Since being stopped by George Foreman over three years earlier Kirkman had won 10 fights in a row including a victory versus Jimmy Ellis. Boone was taking an un-necessary fight with Al Jones before his already scheduled and important match with Ken Norton.
After being KO'd by Jones Kirkman went on a four bout losing streak and was no longer a contender.

 

Agreed that one was extremely shocking

 

then buster vs tyson fits the bill

 

Barrera vs Naz.

Naz was the favourite going into that fight and Barrera him a schooling good and proper.

 

In the UK Naz was a 1:8 favourite to win. You've got to remember that Barrera was moving up to fight at 126lb for the first time. He was fighting Naz who'd reigned supreme at 126 for the best part of 5 years and was known to have devastating KO power.

 

I'm not too sure but it may have been something to do with Barrera having to move up in weight for the fight and Hamed having been dominating everyone else up to that point.

 

Carlos Maussa vs Vivian Harris anyone?

Maussa was/is a construction worker or something like that and Harris was considered to be one of the best. Harris tried to impress the audience by wanting to get rid of the guy soon. But Maussa appeared having a granite chin and knocked out Vivian.

Not a real schooling though. But maybe worth mentioning it.

 

Honeyghan - Curry...an astounding performance and result

 

monaco vs. mcbride:bbb