Top-seeded Lee Chong Wei returned from an injury break to squeak into the last 16 of the Olympic tourney.
The Malaysian, who tore right ankle ligaments at the Thomas Cup in late May, beat Ville Lang of Finland 21-8, 14-21, 21-11.
Defending champion Lin Dan of China eased through his opener against Scott Evans of Ireland 21-8, 21-14. For the women, world champion Wang Yihan and No. 2-seeded Wang Xin also advanced with ease.
Also, Wang Yihan opened her first Olympics with a 21-8, 21-16 win over Michele Li of Canada, and Wang Xin beat Rena Wang of the United States 21-8, 21-6.
Three-time Olympic champions Pavol and Peter Hochschorner finished second in the qualifying heats in the men's canoe-kayak C2 doubles competition.
The Slovakian twin brothers, seeking a fourth consecutive Olympic gold, qualified behind the French pair of Gauthier Klauss and Matthieu Peche.
In the women's K1 singles, Maialen Chourraut topped the qualifying in 98.75. Britain's Lizzie Neave was second, only 0.17 behind.