Holders Estudiantes beat San Luis of Mexico 3-1 to qualify 4-1 on aggregate and Cruzeiro, last year's runners-up, eased through with a 3-0 away win over nine-man Nacional in Montevideo for a 6-1 aggregate victory.
Nacional, overwhelmed by Cruzeiro, had 19-year-old central defender Sebastian Coates sent off in the 53rd minute and striker Gustavo Varela in the 69th.
Corinthians took a two-goal first half lead with a David own goal and a Ronaldo header but failed to protect the advantage and ultimately a 2-1 victory fell short for the club looking to win the trophy for the first time in their centenary year.
Striker Vagner Love scored early in the second half for the visitors to dash Corinthians' hopes and 1981 winners Flamengo qualified on the basis of their 1-0 win in the first leg at the Maracana in Rio de Janeiro last week.
"We had the benefit of the rules and got result we needed. This is the tastiest defeat of my career," an elated Vagner Love told reporters.
"We weren't paying attention at the start of the second half. We fought, gave of our best and I think we deserved better luck. As I see it Corinthians were better (than Flamengo)," former Brazil striker Ronaldo said.
In Montevideo, Thiago Ribeiro, a hat-trick scorer for Cruzeiro in the first leg against Nacional in Belo Horizonte last week, set them on their way to victory again with a 29th-minute strike. Diego Renan and Gilberto added second-half goals.
Cruzeiro will meet fellow Brazilians Sao Paulo in the quarter-finals, while Flamengo are up against Universidad de Chile or Alianza, whose second leg is on Thursday in Santiago with the Chileans 1-0 ahead.
Estudiantes, for whom midfielder Leandro Benitez scored twice, could meet fellow Argentines Banfield in the quarter-finals unless Brazil's Internacional recover from a 3-1 deficit when the teams clash in Porto Alegre on Thursday.
