Carmine Tommasone became the first professional boxer to win a bout at the Olympics on Saturday.
The Italian was too good for Mexican Lindolfo Delgado in the preliminaries of the men's lightweight in Rio de Janeiro.
Local hope Michel Borges was a winner in the light heavy, while Patrick Lourenco had no such luck in the light fly.
Brit Joseph Cordina, bronze medallist at the 2014 Commonwealth Games, beat Charly Suarez in the light.
Tommasone took centre stage and the 32-year-old delivered, claiming victory after judges scored 30-27, 30-27 and 29-28 in his favour.
He became the first professional boxer to win a bout at the Games.
Borges beat Hassan N'Dam N'Jikam, while Lourenco lost out to Yurberjen Martinez.
On a day of mostly one-sided bouts, Cordina had a hard-fought win, with two of three judges scoring it in his favour.
"Maybe the crowd influenced the judges a little bit because they were quite noisy, the Filipinos. And then Suarez was showing off a little bit in the last round. I don't why because every time he lunged in with a shot, he was missing, so I don't where he was getting all his confidence from." - Cordina was far from impressed with his tight win, or his opponent.
"I did notice that I had a lot of people that were going against me but I had my family out there, my team-mates out there. I have about 20 people coming to back me, I even have a dentist coming, just to support me, but hopefully he'll help me out on my teeth if I need it." - American Carlos Balderas said after seeing off Berik Abdrakhmanov.
"It was a rough fight, a lot of clinching, but it was my first fight in the ring getting the rust off. I will definitely look better in my next fight." American Nico Hernandez promises improvement after beating Manuel Cappai.
The men continue in the preliminaries on Sunday, with Thai pro Amnat Ruenroeng among those beginning their campaigns.