It was though the football Gods were trying to cool off a city that is set to explode with volcanic ferocity after weeks of unbearable tension.
In case you missed it, the first leg is now kicking off at 6am Monday morning (AEDT) - LIVE, FREE and in HD on SBS / live streamed online via The World Game website and app.
But the deluge has done little to curb the mounting tension in Buenos Aires.
After all, this is a match that is 58 years in the making. Boca Juniors and River Plate - so famous their full names are usually abbreviated to the first word - aren’t just playing to be crowned champions of South America.
This has the traits of a title-fight where the winner is crowned champion until the next time they meet on this stage. As that might never happen, the triumphant team will effectively earn the status of victor-in-perpetuity. The eternal champion.
This is a game that will be the subject of documentaries, chants and graffiti; possibly even music, art and books. The winner will celebrate for decades. The losers? Don’t ask.
Ordinarily, you’d think this was all hyperbole. Unless you’ve been to Buenos Aires, a city of 21 professional clubs, 14 of which play in the Primera Division, seven of which boast stadiums of 45,000 or greater. You could comfortably host a FIFA World Cup within the city limits.
Neither of these two sides are even the most successful continental team in Buenos Aires. That’s Independiente, seven-time champions. It’s a fact that colours the canvas even more: this city is football’s own Mecca.
But “BA” is stark in its complexity. The elegance and sophistication of Belgrano, Palermo and Recoleta (close to River's Estadio Monumental) is world-renowned; the rougher-than-rough port areas (encircling Boca’s La Bombanera) a haven for crime of all kinds.
It is a city of boom and busts. Right now, it is the latter. A year ago, one Australian dollar yielded roughly 13 pesos. Today, it gets you 26 (even as much as 30 in September). Valuations of real estate only come in US Dollars. As luck would have it, bank loans are only offered in pesos. Interest rates are off the charts.
And so football is offering what it always does best: the promise of happiness. A deflection from the menacing reality.
Yet while the Copa Liberatodores is largely unnoticed outside South America, this local final has seized the world’s attention.
We’ve had derbies in major continental finals before - Madrid has done it twice recently - but never in the Libertadores. It’s only the third time two teams from the same country (Brazil offered both 2005 and 2006) have made the final.
River had to overcome Independiente in the quarter-finals just to get to the final four. This famed duo then had to take out top Brazilian opposition - Palmeiras and Gremio - in the semi-finals to produce this mythical ending.
Adding to the narrative is that both sides have endured embarrassing periods in the past decade. River were actually relegated in 2011; Boca finished 19th of 20 teams in the Torneo Final in 2013, winning only three of 19 games and scoring the equal fewest goals of any team in the league. Relegation was avoided but the shame stuck.
As it happens, both teams are battling in mid-table in the league this season. Expect major revivals once their Libertadores’ duties are done. Boom and bust applies on the field, too.
Boca have the edge in star power, with a front third to die for. Carlos Tevez, Cristian Pavon, Dario Benedetto and Mauro Zarate have enjoyed global fame, although Ramon Abila has been keeping Tevez benched of late. From midfield, Fernando Gago could still play for any team in Europe.
But Boca’s attack can’t have it all their own way. In the knockout stages, River have conceded just three goals in six games. Let it be lost on nobody that Jonatan Maidana was moulded into a star by Boca; now he’s their rivals’ top man in defence.
Evergreen 36-year old Leonardo Ponzio controls River’s flow, while the powerful Lucas Pratto and the slinky Ignacio Scocco offer threats that will delight neutrals - though neither is assured of a start.
Delightfully, and fittingly, the managers were iconic players for their respective teams. Marcelo Gallardo at River, Guillermo Barros Schelotto for Boca. Just imagine the pressure they both face. Civic and sporting immortality awaits one of them.
Boca may be favourites on paper but with the second leg at the Monumental, River have a strategic advantage. But we simply do not know what will happen. Largely because we have never seen it before.
Truth be told, none of us will probably ever see it again.
