Empty seats at Rio Olympics (Getty Images)
The sight of vast swathes of empty seats at the 60 000 capacity Olympic stadium in Rio will have embarrassed organisers at the first action of the Games.
Nilla Fischer bundled home the only goal of the game after South African goalkeeper Roxanne Barker fumbled a cross to give the Swedes a perfect start.
A much bigger crowd is expected at the same venue later Wednesday when hosts Brazil take on China in the other game in Group E.
Both the men's and women's football tournaments are being staged in six cities across Brazil that also hosted the 2014 World Cup.
World champions and four-time gold medallists the United States begin their campaign later in Belo Horizonte against New Zealand before Colombia and France also face off in Group G.
Two-time world champions Germany are expected to sweep aside Zimbabwe in their Group F opener.
2015 World Cup quarter-finalists Canada and Australia complete a busy first day of action in Sao Paulo.