On March 31, 1959, Peralta suffered his first loss as a professional, a ten-round decision defeat to then reigning South American light heavyweight champion Luis Ignacio in São Paulo, Brazil in a non-title bout.

After winning his next five fights, including four in Uruguay, Peralta faced Mauro Mina, in a widely expected light heavyweight bout between two South Americans.

Peralta was given his first chance at winning a belt when he fought Jose Giorgetti, on August 4, 1962, at Mar del Plata for the Argentine Heavyweight title.

The biggest win of his career came during that streak, when he outpointed world light heavyweight champion Willie Pastrano over ten rounds at Miami, Florida on September 20, 1963, in a non-title bout.

The truth is a cut opened in the second Thornton fight re-opened during Peralta's challenge of Pastrano and the bout was, to some hastily, to others justifiably, halted.

After the Bonavena rematch, Peralta faced George Foreman in a fight that was televised in the United States, on February 16, 1970, once again at Madison Square Garden.

Foreman held an aura as an awesome knockout artist but Peralta doggedly went ten full rounds with the future two-time world Heavyweight champion.

But Peralta's boxing skill and mobility showed that Foreman was open to fast well-placed counters and that he could weaken late in a fight.

Peralta's next bout came when he beat future world Light Heavyweight title challenger Piero del Papa, by a fifth-round knockout on June 6 at Montevideo.

His next bout marked his European debut, when he defeated Herbert Wick, exactly sixteen days after the fight with del Papa, by a second-round knockout in Barcelona, Spain.