The first part of a huge double-header went Barca's way in a 2-0 away triumph as Ousmane Dembele and Lionel Messi scored to take Ronald Koeman's men to second.
The Blaugrana are now only two points behind league leaders Atletico Madrid, albeit having played two games more, and have their confidence renewed heading into Wednesday's home Copa semi-final second leg against Sevilla, where they must overturn a two-goal deficit.
A 2-0 defeat in the first leg earlier in February had contributed to a downbeat mood at Camp Nou, combined with a humbling Champions League defeat to Paris Saint-Germain and a modest league position.
But Barca stalwart Pique is now feeling positive, even though Pedri and the returning Ronald Araujo appeared to suffer injuries.
He explained: "There is a league [title race]. We have seen much worse things. We are not in a perfect situation, but there is confidence. We hope we can do something.
"Everything is in the head. During my time at Barca, we have had many moments of these injuries, but if the team is good in the head, it does not matter who plays. It is a matter of having team spirit.
"If we turn it around in the tie on Wednesday, the season changes completely.
"It's a matter of looking for that life that allows us to fight for titles until the end, which is what Barca are asked to do."
After the Copa first leg kickstarted a run of one win in four for Barca, they have enjoyed back-to-back victories and were good value for Saturday's success, Koeman's first against Sevilla in his coaching career.
Sevilla did not muster a single first-half attempt and finished with only four in total, while Barca had three big chances - from which Opta would expect them to score - and netted two of them.
"The last times I have come to speak [to the media] have been painful moments," Pique said. "Today I am very proud of the team. We came from hard blows and the team has risen.
"Today I think we have shown that the team is still very much alive, that it has the squad to compete and that on Wednesday we will fight."
Araujo, back having been out since prior to the February 10 trip to Sevilla, was only involved due to Pique's substitution on 67 minutes.
Pique, whose seven aerial duels contested was more than any other Barca player, was not injured, though, rather still working to recover full fitness following a three-month layoff with a knee injury.
"It is a small inconvenience," he said. "I had not played for a long time and I am playing more than expected.
"It was agreed that this would be the minute. I am very happy to continue participating."