Luan struck late as Gremio ended Flamengo's sequence of five consecutive wins with a 1-0 victory.
On Saturday, the 21-year-old forward broke the deadlock in second-half injury time when he dribbled past three Flamengo defenders and fired a low shot past goalkeeper Marcelo Grohe at the Maracana stadium, reported Xinhua.
The result gave Luiz Felipe Scolari his first away victory since taking charge of Gremio in July after being sacked as Brazil coach.
Gremio are now fifth in Brazil's Serie A standings while Flamengo have dropped to 10th at the season's halfway point.
Also, David Braz struck twice in Santos' 3-1 victory over Vitoria at the Vila Belmiro stadium Saturday.
