Cuba's Arlen López continued his campaign to reclaim the middleweight title he earned in 2015 with a victory against Dominican Republic's Euri Cedeno at the International Boxing Association (AIBA) World Championships here.
As the reigning current Olympic and Pan American Games middleweight champion, López is the top seed in the division.
He got past Cedeno 4-1 to book his place in a quarter-final clash against Russia's Gleb Bakshi, with the home favourite edging past Ireland's Michael Nevin 3-2.
Fourth seed Salvatore Cavallaro of Italy recorded a unanimous victory against Vitali Bandarenka of Belarus, setting up a clash with the division's fifth seed, Hebert Da Conceicao Sousa.
The Brazilian survived a scare against Fanat Kakhramonov of Uzbekistan, narrowly defeating his opponent 3-2.
Competition in the middleweight is due to continue on Wednesday (September 18).
The opening bouts of the super heavyweight division followed, with Commonwealth Games champion Frazer Clarke of England beginning his campaign with a win.
He unanimously beat Vladan Babić of Serbia and is set to face France's Mourad Aliyev next.
Maksim Babanin delighted the home crowd when he delivered a knockout blow to Andy Christopher Andall of Grenada in the first round, with the referee stopping the contest and giving the victory to the Russian.
Armenia's Gurgen Hovhannisyan is set to be Babanin's next opponent, having overcome Aleksandar Mraović of Austria 5-0.
There was an upset in the final bout of the day, with Justis Huni of Australia knocking the division's fourth seed out of the competition.
He was given a unanimous win against Cristian Camilo Salcedo Codazzi of Colombia.
Next up for Huni is due to be Trinidad and Tobago's Nigel Paul, who defeated Muhammed Aydin of Turkey by the same result.
The second round of the super heavyweight class is scheduled to take place tomorrow.
There will also be action in the flyweight, light welterweight, heavyweight, featherweight, welterweight and light heavyweight.