1231 GMT March 28, 2020
Since that fateful night in Paris, Barcelona has regained both leadership of La Liga and its confidence ahead of the last 16, second leg, AFP reported.
And despite the news that Luis Enrique will no longer be its coach next season, Barca showed no negative effects as Lionel Messi led a 5-0 destruction of Celta Vigo on Saturday in arguably the club's best performance of the season.
"Hopefully we can produce a miracle," said midfielder Ivan Rakitic.
No side has ever overturned a 4-0 deficit in the knockout stages of the Champions League.
"Evidently, it is very difficult, we are not stupid," accepted Enrique.
Yet, by announcing his decision to go at the end of the season, Enrique has calmed the waters that raged as Barca was torn apart by a faster, more determined and precise PSG, which enjoyed the glorious European night it had long waited for since Qatar Sports Investments starting pumping millions into the club six years ago.
Not everyone believes the tie is over, though.
"My advice to you, knowing Luis and the players a little, is not to talk too much, because they will be back and prove you wrong," former Barca and now Manchester City manager Pep Guardiola had said about the first leg.
At the time very few, even in Barcelona, believed that. Now, 21 days on, they very much do.
Enrique spoke on Friday of the "relief" at ending speculation over his future.
And in following up a 6-1 thrashing of Sporting Gijon with the dismantling of Celta at the weekend, Barca had the air of a team with a weight removed.
"If the stars align we can turn that game around," Enrique added as he announced his decision last week.
"With this team you have to always believe," said Barca sporting director Robert Fernandez.
"We have a hugely difficult result against us against a magnificent team, but in football anything can happen."
If there is one side in world football with the firepower to dream it is Barcelona.
On top of Messi, Neymar has come back into goalscoring form in the past week, whilst Luis Suarez already has 26 goals this season.
Indeed, the results from over a third of Enrique's home games as Barca coach would be good enough to at least force the game to extra time.
That record includes all three of Barca's Champions League games this season as it dismantled Celtic (7-0), Manchester City (4-0) and Borussia Moenchengladbach (4-0) by a combined score of 15-0.
Meanwhile, Suarez is seeking inspiration from one of the best displays of the Enrique era as last season Barca thrashed eternal rival Real Madrid 4-0 at the Santiago Bernabeu with Messi only available for the last half hour on his return from injury.
"If we were capable of scoring four goals against Madrid at the Bernabeu, why can't we score four against Paris at the Camp Nou," the Uruguayan told Spanish radio station Onda Cero.
"If we score two then they can begin to get nervous that we can pull it off because we know we are capable of it."