After a successful fourth defense, Argüello moved up in weight to challenge world junior lightweight champion Alfredo Escalera in Bayamón, Puerto Rico, in what has been nicknamed "The Bloody Battle of Bayamon" by many. Escalera had been a busy champion with ten defenses, and he had dethroned Kuniaki Shibata in 2 rounds in Tokyo. In what some experts (including "The Ring" writers) consider one of the most brutal fights in history, Escalera had his eye, mouth and nose broken early, but was rallying back in the scorecards when Argüello finished him, once again in the thirteenth round.