Gabriel Valenzuela quickly capitalized on an opportunity Thursday night that he received on short notice.

The Mexican junior welterweight knocked out fan favorite Yves Ulysse Jr. just 52 seconds into their 10-round fight at Casino de Montreal in Montreal, Quebec, Canada. Valenzuela drilled Ulysse with a short right uppercut that knocked Ulysse on his side just 34 seconds into their fight.

Ulysse attempted to get up and fell down again. He reached his feet before referee Martin Forest counted to 10, but he was in no condition to continue.

Forest realized Ulysse shouldn’t fight on, wrapped his arms around the wobbled Ulysse and halted the action.

Guadalajara’s Valenzuela, a late replacement for 2008 U.S. Olympian Javier Molina, improved to 26-3-1 and recorded his 16th knockout.

Montreal’s Ulysse slipped to 22-3 (12 KOs). The 34-year-old contender lost by knockout for the first time in his nine-year professional career.

ESPN+ streamed Valenzuela’s upset victory as the co-feature before Quebec-based super middleweight Erik Bazinyan boxed American Alantez Fox in the 10-round main event.

Keith Idec is a senior writer/columnist for He can be reached on Twitter @Idecboxing.