Although the opening ceremony takes place on Friday, the football competitions begin ahead of time with six women's matches on Wednesday and another eight men's games on Thursday.
The opening action at Rio's Olympic stadium was lacklustre with few clear chances.
Nilla Fischer scored Sweden's winner after 74 minutes, bundling the ball into the net with her knee after the South African keeper failed to hold a cross.
Sweden were superior, particularly in the first half, but could not turn possession into goals.
Sweden players Caroline Seger (2-L) and Lotta Schelin (2-R) vie for the ball with South Africa players Lebohang Ramalepe (C) and Noko Matlou (R) during the Rio 2016 Olympic Games women’s First Round Group E football match Sweden vs South Africa, at the Ol
Image credit: AFP
The result means South Africa have yet to win an Olympic football match in their four finals appearances.
The second game in Group A takes place later on Wednesday when home side Brazil, seeking their first Olympic gold after two silver medal performances, take on China.
Holders and No. 1 ranked side the United States play New Zealand at night in Belo Horizonte.
The men's competition begins on Thursday, with eight games, including Brazil against South Africa and holders Mexico versus Germany.