I think your talking about "Locomotora" Castro vs. "Action" Jackson I...

Not only is it a great knock out, it's a great fight and is argueably the greatest comeback in boxing history. Up there with Moore-Durelle, JCC-Taylor, Reagan-Dempsey and Chacon-Limon IV.

John D. Jackson was out boxing and beating the crap out of Jorge Castro for 8 full rounds and most of the 9th and then it happened...

http://www.youtube.com/watch?v=5gNJsdRDQYw