Has to be Eubank-Watson II. Just has to be. Eubank had lost every minute of every round, gets floored for the first time in his career at the end of the penultimate round, and rises before the count to unlease an uppercut from hell that literally cripples Watson. Real Rocky stuff.
A bizarre comeback was David Izon-Derrick Jefferson. Izon was taking such a beating that even Merchant was calling for it to be stopped. Then Jefferson suddenly gasses and gets stopped. It was like a longer version of Klitschko-Brewster 1, or how revisionist history has described Ali-Foreman (in reality Ali was tagging Foreman from the get-go). Izon pulled a Homer Simpson.
It has to be foreman ko Moorer after Foreman was losing basically every rounds and Foreman was 45 years old.