Josesito Lopez caused a huge upset after he stopped Victor Ortiz in their welterweight clash in Los Angeles after stepping up as a late replacement when Andre Berto failed a drugs test.
Lopez was stepping up in weight to take on Ortiz and the challenger was behind on the scorecards when he broke his opponents jaw in the ninth round and 'Vicious' retired on his stool.
Ortiz was due to face Saul Alvarez, who was in the crowd watching on, in his next contest but those plans have now been thrown out of the window after a shock loss.
The power shots had seemed to be coming from Ortiz for most of the fight as the pair often exchanged shots but as the contest continued Lopez seemed to grow in confidence.
He was caught with an illegal blow to the back of the head in the fifth round, but showed real heart and desire to stay in the fight and continue to trade with the heavy handed Ortiz.
Ortiz did lead on the scorecards 86-85, 87-84, 88-83, but at the end of the ninth round he struggled to close his mouth and informed the referee that he was not able to continue.
"I told everyone I was going to shock the world," Lopez said. "Today's my day. Today's my day.
"I'm excited. I had to fight the fight of my life to win. I knew I caught him every round. I might not have thrown the majority of the punches, but the ones I was throwing, I knew I was connecting."