They were there to celebrate the victory over Colombia that earned Brazil a heavyweight semi-final clash with Germany. Folks danced, drank, set off fireworks and simply enjoyed being part of a 200-million strong nation invested in the fortunes of the Selecao.
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Then, word began to spread in that incredulous way that often happens when crowds assemble. Neymar was in hospital. Tests revealed his back injury was worse than imagined. A vertebra was damaged. His tournament was over.
Joy turned into something else. Not despair, that would have been too trite. Neither was it resignation: this is still Brazil, this is still their World Cup.
Rather it was a kind of frustration, a realisation that this was turning into some kind of Sisyphean exercise. The more they rose, the higher the bar.
And Brazil won't just be facing Germany without Neymar. Their skipper and defensive stalwart Thiago Silva will also be out, suspended after picking up a foolish yellow card when trying to disturb Daniel Ospina's goal kick.
The damage to Neymar was done in a collision with Juan Camilo Zuniga during the 2-1 win, when the defender's knee slammed into the striker's back. It wasn't a dirty foul necessarily and Zuniga apologised afterwards in any case, but the scapegoating was inevitable.
Fingers were pointed at the referee, Carlos Velasco Carballo, as well. He seemed to lose control of a game that turned increasingly physical, possibly in part due to his reluctance to caution players. By the time Silva saw yellow in the 64th minute no fewer than 41 fouls had been committed.
It is true that Massimo Busacca, head of Fifa referees, had urged officials before the tournament to use cards only when absolutely necessary. But we had passed the "absolutely necessary" point much earlier, as Neymar and his Colombian counterpart James Rodriguez were pummelled seemingly continuously by the opposition.
Now, the ball is in Luiz Felipe Scolari's court. The Brazil coach sold himself as a "can't miss" appointment, what with the fact that he's already won a World Cup and his persona - both folksy and country tough - appealed to large swaths of the population.
But the team he put together, based on staunch physical defending on one end and Neymar sorting things out at the other, failed to win over the critics. And, last Thursday, he erupted, telling the media to "go to hell" after he was upbraided for giving certain journalists preferential treatment.
His plan needs a makeover without Neymar. Dante can come in for Silva and while there will be an obvious drop in quality, experience and charisma, Brazil will still have a solid defensive partnership.
It is up front where he will need to come up with a scheme in double quick time; one that is less reliant on individual brilliance and, instead, emphasises teamwork. He has 48 hours to do it and, given his track record, few are holding their breath.
Brazil's opponents on Tuesday will be Germany, who dispatched France with greater ease than the 1-0 scoreline suggests. Jogi Loew's side have blown hot and cold this tournament and had suffered scares of their own, against Ghana in the group stage and Algeria in the round of 16.
Against the French - one of the few sides to have played consistently well throughout the tournament - they went back to basics. Philipp Lahm returned to right-back, with Jerome Boateng partnering Mats Hummels and the old-school partnership of Bastian Schweinsteiger and Sami Khedira reunited in midfield.
It meant more pace and agility in the backline, more bite in the middle of the park and, most of all, a stiffer, more direct counter-attack instead of the fancy possession game Loew had tried to implement. It worked a treat, not least because Germany got the early goal.
It is too early to say whether this is a permanent tweak or maybe simply a case of the Germans adding some variety to their style.
"It's good to be able to play more than one way," Loew said, stating the obvious, but also reminding us that Germany are more multi-faceted than one thought.
What is obvious is that, after having reached at least the semi-finals in each of the last five major tournaments they played in, going back to the 2006 World Cup, they are now poised to go one step further.
What we know for sure about Luis Suarez's future is that Barcelona and Liverpool are talking and the deal is about done. All parties are being vague over the actual fee, but you would expect it to be in the £60-£70m range.
The number will depend on whether Alexis Sanchez is part of the deal going the other way. That's the nice thing about player-plus-cash deals: you can put (almost) whatever number you like on the guy in part-exchange and make the deal seem as lucrative as you like.
What is obvious is that barring some kind of cataclysm, Barcelona will feature a fantasy football frontline of Suarez, Lionel Messi and Neymar, AKA, the best player in the Premier League, the best player in the world and the guy who, until Friday night, looked on his way to being the best player for the world champions.
As for Liverpool, Brendan Rodgers is determined to accumulate attacking talent. Sanchez obviously wouldn't be a like-for-like replace-ment (and, in any case, he has an agreement in principle with Arsenal, though the clubs have yet to talk).
But he would bring still more creativity, verve and quality to a unit that already includes Raheem Sterling, Daniel Sturridge and Philippe Coutinho, plus new signing Emre Can, all evidence that last season's attacking pyrotechnics weren't just dictated by the personnel available, but rather fit in to the Ulsterman's vision. Whether it works - or whether the resources aren't best allocated elsewhere, like at left-back or in central midfield - remains to be seen. But entertainment levels appear unlikely to subside at Anfield next year.