Great Britain's Natasha Jonas topped American Quanitta Underwood in a lightweight bout Sunday, when women's boxing made its formal debut at the Olympics.
This is the first games at which women's boxing has been part of the program, and all three classes got underway.
Jonas, a bronze medalist at the world championships, earned a 21-13 decision against Underwood. Next up for Jonas is a quarterfinal bout against top-seeded Katie Taylor of Ireland. Taylor received a bye into the quarterfinal round.
Underwood was the lone U.S. women's boxer to fight Sunday. Flyweight Marlen Esparza and middleweight Claressa Shields both received byes to Monday's quarterfinal rounds.
There was also quarterfinal action in the men's bantamweight and heavyweight draws Sunday.
Cuba's Lazaro Alvarez Estrada, the top bantamweight seed, defeated Brazil's Robenilson Vieira de Jesus by a 16-11 margin. He will fight fifth-seeded John Joe Nevin of Ireland.
Great Britain's Luke Campbell, the No. 3 seed, also advanced to the semis with a 16-15 decision against No. 6 seed Detelin Dalakliev of Bulgaria. He will fight Japan's Satoshi Shimizu.
In heavyweight bouts, the top three seeds -- including No. 1 Oleksandr Usyk of the Ukraine -- moved into the semis.