Carlos Monzon vs Gratien Tonna

On December 13, 1975, at Paris's Nouvelle Hippodrome, Carlos Monzon's WBA middleweight title defence against Gratien Tonna ended in controversy, continuing Tonna's pattern of disputed finishes in championship bouts. The fight, Monzon's 100th professional contest (87-3-9, 1 NC), carried purses of $160,000 for the champion and $25,000 for the challenger.

Tonna, weighing 159½ pounds to Monzon's 159¼, landed a clean left hook in the opening round but failed to build on this early success. Monzon established control in round two with straight rights, creating visible damage under Tonna's right eye by the third round. The Frenchman resorted to rabbit punching, drawing multiple warnings from referee Waldemar Schmidt.

The finish came at 2:02 of round five when Monzon landed a right hand that dropped Tonna to his knees. The challenger remained down for Schmidt's total count, then immediately rose, claiming an illegal blow to the back of the head. Schmidt contradicted this claim, stating the punch landed at the base of the jaw and that Tonna "could have gotten up."

The ending mirrored Tonna's recent loss to WBC champion Rodrigo Valdes, where he had also claimed a foul. This defeat made him among the few fighters to lose to both recognized middleweight champions. Monzon, undefeated since 1964 and making his twelfth successful defence, expressed interest in facing Valdes next "to prove that there's only one middleweight champion."