Lionel Messi came out to defend Philippe Coutinho amid criticism over the Brazilian's recent form.
He was eventually taken out of the match in the 60th minute, with Ernesto Valverde opting to bring on defender Nelson Semedo in his stead.
Coutinho has proven a frequent target of the Camp Nou crowd, earning boos in recent weeks before responding with a stunning goal against Manchester United and a message back to the supporters in the form of a celebration.
But Coutinho's struggles were once again booed on Wednesday, and Messi says there is no reason to criticize his team-mate.
"We are in a defining moment and it is not time to criticize anyone," Messi told Movistar Plus following Wednesday's victory.
"It is time to make everything happen as we talked at the beginning of the season.
"It is ugly to see a team-mate get booed like that, we must all be together and support."
Coutinho has been locked in a battle with Ousmane Dembele throughout the season as the two wingers have competed for the right to play alongside Messi and Luis Suarez in the Barca attack.
Dembele came into the match in the 93rd minute, replacing Suarez, but failed to capitalize on a golden chance late on.
Given a chance to make it 4-0, the French forward scuffed his shot and, while Messi believes that wasted opportunity was a frustrating one, the Argentinian star says he feels good about his team's performance.
"The last (chance) was very clear, the 4-0 would have been better than the 3-0," Messi said.
"We know it's a good result but it's not finished because we're going to a tough stadium.
"We're happy with the great game we played today."
The two teams will meet once again at Anfield as Coutinho and Suarez return to their former home next Tuesday for the second leg of their Champions League semi-final.
Before that, though, Barca will face Celta Vigo in league play on Saturday.