The two sides will play the first ever final to be contested over just one leg following the disturbances that occurred ahead of the 2018 final.
As the famous song goes, the Copa Libertadores is an obsession for River, who have been in the final on six occasions and view this stage of the competition as something of a birthright.
Nicknamed 'Los Millonarios', or 'The Millionaires', the Buenos Aires club have always regarded themselves as top of the tree in South American football in terms of affluence, both on and off the pitch.
Currently sitting in fourth place in the Argentina Primera Division, just one point off leaders and bitter rivals Boca Juniors, winning consecutive Libertadores titles would serve as a reminder of their pedigree for claiming major trophies.
They will not, on the other hand, want this year's final to be marred by what happens off the pitch, as was the case when the 2018 final was postponed due to attacks on the Boca team ahead of the second leg, which ended up being played in the neutral venue of Madrid.
However, with this game now just a one-off event in a neutral location, pitting Buenos Aires against Rio de Janeiro, South America will likely be treated to a spectacle befitting of its rich footballing culture.
While River holds the reputation of wealth and privilege, Flamengo are a club that belong to the slums of Rio.
The Argentine side are all too familiar with this stage of the competition whereas Flamengo, under the highly experienced Jorge Jesus, enter what will be just the second Libertadores final in their history and their first since 1981.
It is often remarked how any Rio resident can tell when Flamengo have scored by hearing the numerous celebratory gunshots emanating from the favelas, and if they reach the holy grail of South American football for the first time since the days of Zico on Saturday, then the explosions will be heard all across Brazil.
This is by no means a David and Goliath affair, though, given that Flamengo are currently 13 points ahead of their nearest rivals in the Brasilerao Serie A and are expected to hit Marcelo Gallardo's side with an aggressive, attack-minded style.
Spearheaded by former Inter Milan forward Gabriel Barbosa, who has 29 goals in 37 appearances this year, Flamengo will see this game as much more than a cup final, but indeed as a chance to write themselves into history.
Recent River Plate form: DLWWLW
Recent Flamengo form: DWWWDW
For Flamengo, Jesus will be glad that Barbosa's red card against Gremio last weekend does not impinge on Saturday's final, with the Brazilian expected to lead the attacking line.
River Plate possible starting lineup:
Armani; Montiel, Martinez, Pinola, Casco; Perez, Palacios, De La Cruz, Fernandez; Borre, Suarez
Flamengo possible starting lineup:
Alves; Rafinha, Caio, Mari, Luis; Gerson, Arao, Ribeiro, Reinier, Henrique; Barbosa
We say: River Plate 0-1 Flamengo
Predicting the scoreline for a final, especially one of this magnitude, is an essentially impossible task, such is the raw energy in a game whose meaning, as always, goes beyond football itself.
Playing their first Libertadores final in 38 years and cruising at the top in Brazil, we get the sense that this is Flamengo's moment.