Ireland's Jenny Lehane had a unanimous victory over Venezuela's Diana Mastre at the World Boxing Cup Brazil.
The Meath fighter, who had received a bye into the last 16, won on all five judges' scorecard after the 54kg bout.
Lehane, who fights for a medal on Thursday against Serbia's Sara Cirkovic (9.45pm Irish time), told Boxing Ireland: "Feeling good, always good to get the first one under way. So, hopefully, build on today and be back even better tomorrow.
"I definitely started out a bit unsettled, I think. First day nerves. I held on to my composure and felt more relaxed in the second round and it showed."
Jude Gallagher from Tyrone was withdrawn following a medical assessment before his scheduled fight with Salim Ellis-Bey.
He handed his USA opponent a walkover in the last-16 stage of the 60kg category.
Gallagher had beaten Kazakhstan's Zhanseri Kosherbayev is his opening bout in Foz Do Iguaca.
Louis Rooney was defeated by Morocco's Issam Bensayar in their 50kg bout. The Belfast man was beaten in all three rounds.
Evelyn Igharo lost to former pro boxer Citlallo Vanessa Ortiz from Mexico on a split decision.
The Dundalk boxer was ahead after round one of the 70kg fight but four judges went the way of the Mexican.
In addition to Lehane, three more Irish boxers will contest last-16 bouts on Thursday.
Daina Moorehouse takes on Poland's Natalia Kuczewska (3.45pm), world bronze medalist Patsy Joyce faces Tajikistan's Meroj Sufijonov (4.45pm), and Dean Clancy meets Mexico's Hugo Barron in the next match-up.
