Brazil's fans jeered their own team and saved their applause for Iraq after the two sides drew 0-0 in their Olympic clash in Brasilia.
The host nation, who have never won Olympic gold, failed to secure three points in Group A for the second consecutive game after an opening-day draw with South Africa.
The result leaves Brazil tied for second place and they require a victory over Denmark on Wednesday in Salvador to advance and avoid another huge embarrassment at home, two years after the 7-1 loss to Germany in the World Cup semi-finals.
Neymar, the tournament's biggest star, played below expectations for the second straight game, and promising young strikers Gabigol and Gabriel Jesus also struggled.
Voicing their frustrations, the fans chanted 'Marta, Marta' in reference to the five-time world player of the year who has been thriving with the women's national team.
One of Brazil's best chances of the match fell to midfielder Renato Augusto in second-half injury time, but his volley from close range sailed over the crossbar with the goalkeeper already beaten.
Elsewhere, Nigeria became the first team to advance to the quarter-finals by beating Sweden 1-0 in Manaus.
Portugal closed in on the last eight by beating Honduras 2-1 in Rio, while defending champions Mexico beat Fiji 5-1 in Salvador with four goals from midfielder Erick Gutierrez. Argentina topped Algeria 2-1 and Germany scored late in a 3-3 draw against South Korea in Salvador.
Denmark, Brazil's next opponent, defeated South Africa 1-0 in Brasilia.
The host nation, who have never won Olympic gold, failed to secure three points in Group A for the second consecutive game after an opening-day draw with South Africa.
The result leaves Brazil tied for second place and they require a victory over Denmark on Wednesday in Salvador to advance and avoid another huge embarrassment at home, two years after the 7-1 loss to Germany in the World Cup semi-finals.
Neymar, the tournament's biggest star, played below expectations for the second straight game, and promising young strikers Gabigol and Gabriel Jesus also struggled.
Voicing their frustrations, the fans chanted 'Marta, Marta' in reference to the five-time world player of the year who has been thriving with the women's national team.
One of Brazil's best chances of the match fell to midfielder Renato Augusto in second-half injury time, but his volley from close range sailed over the crossbar with the goalkeeper already beaten.
Elsewhere, Nigeria became the first team to advance to the quarter-finals by beating Sweden 1-0 in Manaus.
Portugal closed in on the last eight by beating Honduras 2-1 in Rio, while defending champions Mexico beat Fiji 5-1 in Salvador with four goals from midfielder Erick Gutierrez. Argentina topped Algeria 2-1 and Germany scored late in a 3-3 draw against South Korea in Salvador.
Denmark, Brazil's next opponent, defeated South Africa 1-0 in Brasilia.
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