Pinto, seeded third, was expected to reach at least the semi-finals, but Martinez had other ideas, booking his place in the next round with a split decision victory at the Coliseum Nacional de Ingenieros in the Honduran capital.

Martinez was awarded the bout on three of the five scorecards, while two judges gave the fight to Pinto.

Jorge Luis Vivas, the second seed in the middleweight category, had no such trouble as he beat Raul Sanchez Marte of The Dominican Republic 4-1.

Pinto was the highest-profile casualty on day two of the event as action in the men's weight categories began.

Pan American Games gold medallist Arthur Biyarslanov of Canada safely progressed in the light welterweight category as he swept aside Argentinian Christian Andino.

Biyarslanov, who was born in Russia, made light work of his opponent and reached round two with a unanimous points win.

In the women's flyweight category, double Pan American Games champion and Glasgow 2014 Commonwealth Games bronze medallist Mandy Bujold of Canada outclassed Puerto Rico's Emily Colon.

Bujold, the second seed in the division, produced a dominant display on her way to a comprehensive unanimous success.

She was joined in the next round by American boxer Virginia Fuchs, who proved too strong for top seed Colombia's Ingrit Valencia Victoria.

Fuchs picked up a stunning win over Victoria, who represented her country at last year's Olympic Games in Rio de Janeiro, progressing with a unanimous victory.

As well as gold medals, competitors at the AMBC American Confederation Championships are also vying for places at the men's International Boxing Association (AIBA) World Championships in Hamburg, which run from August 25 to September 3.

Action is due to resume tomorrow, with the event in Tegucigalpa due to conclude on Sunday.