Following last week's 2-2 draw away to Independiente, 10-man Flamengo triumphed 5-2 on aggregate thanks to Gabriel 'Gabigol' Barbosa and two-goal hero Gerson.
All-conquering Flamengo have taken South America by storm under head coach Jorge Jesus, ending trophy droughts domestically and continentally.
After winning a second Libertadores title and first since 1981 in November, Flamengo were crowned Brazilian champions for the seventh time last year, having not claimed the Campeonato Brasileiro since 2009.
Flamengo sealed another piece of silverware on Wednesday in the annual CONMEBOL showdown between the previous year's Libertadores and Copa Sudamericana champions.
Gabigol – who made his move from Serie A side Inter to Flamengo permanent in January – gave the home side a 19th-minute lead after an embarrassing moment for Independiente.
Independiente defender Luis Segovia's header back to Jorge Pinos left his goalkeeper scrambling as the ball struck the crossbar and fell to the feet of Gabigol.
After team-mate Willian Arao saw red four minutes later, former Roma midfielder Gerson doubled Flamengo's lead in the 62nd minute and completed the scoring with a minute remaining following a red card to Independiente substitute Alejandro Cabeza.