Top two seeds Wang Ki-Chun of South Korea and Japan's Riki Nakaya progressed safely through the early rounds of the Olympic judo men's under-73kg category on Monday.
Twice a world champion and Olympic finallist in Beijing in 2008, Wang needed a sudden death period of golden score to beat Nugzar Tatalashvili of Georgia in the first round.
He then submitted Rinat Ibragimov of Kazakhstan while pinning him to the ground.
Second seed Nakaya had little trouble against Kyle Maxwell of Barbados, pinning him for the maximum ippon score (a technical knock-out).
Russian third seed Mansur Isaev and fourth seed Dex Elmont of the Netherlands also made safe progress.
It was a similar story in the women's under-57kg category with world number one Kaori Matsumoto of Japan throwing Slovenia's Vesna Dzukic with an outer sweep (osoto-gari).
But second seed Telma Monteiro of Portugal was stunned in golden score by American Marti Malloy.
Third seed Rafaela Silva of Brazil and France's fourth seed Automne Pavia both progressed from their opening bouts.