Brazil face another embarrassing exit from a tournament on home soil after Neymar slumbered through a second 0-0 draw of Rio 2016 against Iraq.

The Olympic hosts need to beat group leaders Denmark on Wednesday to win to avoid a stunning exit, just two years after their devastating 7-1 World Cup defeat by Germany.

Neymar was expected to ease Brazilian football's wounded pride by delivering a first ever Olympic gold for the five-time world champions.

However, the Barcelona star was eclipsed. And just as in their opening stalemate against South Africa, Brazil were booed from the field in Brasilia on Sunday as they paid for their profligacy in front of goal.

Portugal and Nigeria were the first sides to seal their places in the quarterfinals with victories over Honduras and Sweden respectively.

There were also wins for Argentina, Denmark and Mexico.

In contrast to his display against South Africa when he was labelled "greedy", Neymar was a peripheral figure against Iraq and lost his cool when he fired the ball at Sherko Kareem in the second-half as the Iraqi prevented him from taking a quick free-kick.

Iraq could even have snatched a shock win when Mohanad Abdulraheem's first-half header came back off the inside of the post.

Atletico Madrid's Angel Correa scored and set up Jonathan Calleri's winner as 10-man Argentina got their challenge for a third Olympic gold back on track with a 2-1 win over Algeria in Rio.