Barcelona forward Neymar was unable to help Brazil make a winning start to the Rio 2016 Olympic Games as the hosts were held to a goalless draw by 10-man South Africa in Brasilia on Thursday.

New Manchester City forward Gabriel Jesus hit the post for London 2012 runners-up Brazil.

South Africa's Mothobi Mvala was sent off just before the hour after picking up a second yellow card for a foul.

Group A is a four-way tie on one point after Iraq and Denmark drew 0-0.

A sparse crowd inside the Estadio Nacional Mane Garrincha in Brasilia saw a game full of chances but no goals.

Iraq were denied victory when Saad Abdul-Amir's long-range attempt was saved by Jeppe Hojbjerg.

The men's football tournament started one day before Friday's opening ceremony because of a packed schedule.

Mexico, who won the 2012 Olympics in London, were held to a 2-2 draw by Germany in Group C.

The Mexicans took the lead early in the second half through Oribe Peralta but Arsenal midfielder Serge Gnarby levelled soon after.

Rodolfo Pizarro swept Mexico into the lead again but Matthias Ginter, part of Germany's 2014 World Cup-winning squad, powered home a late header to earn his side a point.

It was a winning start for Portugal in Group D as they beat Argentina 2-0 at the Olympic Stadium in Rio de Janeiro.

Porto striker Goncalo Paciencia opened the scoring midway through the second half, firing home from outside the box.

A goalkeeping error by Geronimo Rulli then sealed the win for Portugal as the Argentina shotstopper let Pite's tame shot squeeze through his legs.