Why was Nelson beating Fenech regarded as such an upset?

[Bright-Eyes]

Not just an upset,but voted Ring Magazines 'The Ring Upset of the Year.'

[Rolling Stone]

considering Jeff Fenech was younger and undefeated and had arguably won their first fight it was somewhat of an upset........

not that great of an upset though

[mickey malone]

considering Jeff Fenech was younger and undefeated and had arguably won their first fight it was somewhat of an upset........

not that great of an upset though

I doubt anyone would argue that Fenech won the 1st fight.. They went toe to toe & Nelson lost at least 8 of the 12 rounds, was out on his feet in the closing 10 seconds and in my opinion was only saved by the bell.. I have to say, it was one of the worst decisions i've ever seen and a draw wasn't a fair result.
Such was Fenech's domination in the 1st fight, and with the return being in Sydney, he was generally expected to stop Nelson.. Very few banked on Nelson altering his style to box, move and slip punches as Fenech swarmed in.. By making him miss he made him gas, and he'd learned that Fenech only knew one way to fight.. Much the same way as Leonard had mastered the style of Duran in a losing effort, Nelson did the same to Fenech and certainly lived up to his nick-name, 'The Professor.'