Who lost to Glass Joe?

He has lost 99 times and has won once, in a freak accidental win against Nick Bruiser, states the Official Nintendo Magazine Punch-Out!! programmer.

Source

From the Wiki:

He has lost 99 times and has won once, in a freak accidental win against Nick Bruiser, states the Official Nintendo Magazine Punch-Out!! programmer.

Looks like it's Nick Bruiser (by accidental victory).