After winning 22 consecutive bouts Duran suffered his first defeat, losing to Jean Josselin via an eight-round decision on June 22, 1970.
De Oliveira, a native of Brazil, won the title via a unanimous decision after a bloody battle which lasted the full fifteen rounds.
On this occasion Duran travelled to Tokyo, Japan to successfully challenge Koichi Wajima for the Lineal and WBA light middleweight titles.
Although Duran rose from the canvas, he was outworked by the faster challenger and lost his title via a split decision in a fight where both boxers finished with bloody faces.
The result was never in doubt, as Mattioli knocked Duran down in the second, fourth and early in the fifth before delivering the final knockout punch late in the fifth round.