David Notoane's South African Olympic team suffered a narrow 1-0 defeat to host nation Japan in their Group A opener at the Tokyo Stadium on Thursday.
Japan dominated large parts of the first-half after Notoane opted to utilise a cautious tactical approach by naming a five-man defence to nullify their opponents.
This meant that Japan, who looked the more dangerous of the two sides, dominated possession with SA goalkeeper Ronwen Williams in impressive form to keep the scores level.
The increasing Japanese pressure eventually told as the host nation took the lead in the 71st minute through midfielder Kubo Takefusa.
Notoane was then forced to change his approach and formation as South Africa went in search of an equaliser.
Despite their efforts South Africa were unable to find the all-important goal as they made a losing start to their Olympic campaign.
South Africa are next in action when they take on France on Sunday, while they are also pooled alongside Mexico in Group A.
Earlier on Thursday, Mexico beat France 4-1.
The top two teams in each pool will qualify for the tournament quarter-finals.