The Brazilian sides were both bidding for their third Libertadores title in Montevideo, Uruguay, and it was Palmeiras that came out on top to become the first side to win the tournament in successive seasons since Boca Juniors did so in 2000 and 2001.
Palmeiras made a flying start, with Raphael Veiga scoring the earliest goal in a Libertadores final since 2008, but at the stadium where it won its maiden title in 1981, Flamengo's second-half dominance was rewarded when Gabriel Barbosa restored parity.
Having scored early in regulation time, Palmeiras repeated the feat in the additional period – substitute Deyverson proving to be the hero.
Veiga's fifth-minute opener was wonderfully worked, with Mayke getting to the byline and cutting it back for the on-rushing midfielder to finish first time.
Aiming to repeat the feat of rival Corinthians, which is still the only team to win the title while going undefeated in the current format of the tournament, 2019 champion Flamengo would then have equalised if not for the reactions of Weverton, who denied Giorgian de Arrascaeta from point-blank range.
After squandering a golden chance to head in from close range, Gabi, Flamengo's hero in 2019, atoned for his miss with a drilled strike in the 72nd minute, catching Weverton out at his near post with unerring accuracy, becoming the first player to score 11 goals in a Libertadores campaign.
Yet a lapse in concentration from Andreas Pereira cost Flamengo five minutes into extra-time. Having replaced Veiga, Deyverson pounced on the Manchester United loanee's loose touch and squeezed a finish past Diego Alves to etch Palmeiras's name on the trophy once again.