The thumping 4-0 victory over the Italians, which sent Barca through to the quarter-finals 4-2 on aggregate, made a mockery of suggestions the club were in crisis and they will look to protect their 13-point lead at the top of the domestic standings when Rayo visit the Nou Camp on Sunday.
An out-of-sorts Barca were reeling after a 2-0 reverse to Milan at the San Siro in last month's last 16 first leg followed by painful defeats to Real Madrid in the Copa del Rey and La Liga.
Inspired by their Argentine World Player of the Year Lionel Messi, they rediscovered their form in spectacular style against Milan and their bids for a third European crown and a fourth Liga title in five years are very much alive.
"It was the day and the match that we needed," midfielder Sergio Busquets said.
"We didn't do it because we wanted to silence the critics, we did it for ourselves," added the Spain international, who turned in an immense performance against Milan in his unheralded defensive midfield role.
"You have a bad time when you lose, so these days have done a lot of good for our confidence.
"But neither did people need to take the situation quite as seriously as they did. All teams have dips in form."
Real, also through to the last eight of the Champions League after eliminating Manchester United, leapfrogged city neighbours Atletico into second in La Liga last weekend and a win at home to struggling Real Mallorca on Saturday would cut Barca's lead to 10 points.
But with only 11 games left, the champions have effectively written off their chances of catching their arch-rivals and their focus is on the Champions League and the Copa, in which they are through to face Atletico in May's final.
Atletico, who dropped their first home points of the campaign in a 1-0 defeat to Real Sociedad last weekend, play at relegation-threatened Osasuna on Sunday.
After their failed campaign to defend their Europa League title, they are concentrating on securing a lucrative Champions League place for next season and are 13 points ahead of Malaga and Sociedad in fourth and fifth respectively.
Coach Diego Simeone, who committed himself to the club until the end of the 2016-17 season by agreeing a new contract last week, said his players needed to rediscover their scoring touch if they are to prosper.
"We found it tough (against Sociedad) to maintain the calm to finish off our attacks in the final metres, which are the most difficult," he told a news conference on Wednesday.
"Now we have to keep pushing to have that fluidity in the final phase," added the Argentine.
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