An early goal from Lamine Yamal set the Spanish champions on the road to victory, before a double from club captain Raphinha took the game away from Unai Emery's team, who had won their first three matches of the competition.
Despite the frustration over the final result, Emery was pragmatic in his post-match assessment as the game offered his players a level to measure themselves against, ahead of facing a key Premier League trip to Manchester United this weekend.
"The result is not good, a lot of things were positive, but it was not enough to get a good result.
"How we are building the team is clear in 90 minutes, but we have young players, talented players and experienced players. We made some mistakes. Over the process we've had here, we have made those mistakes, but then overcame them.
"If we scored one goal with the chances we had in the first half, maybe it would have been different, but we were not clinical.
"I have my opinion on how we can get better, but this experience is very important.
"This is the level we want to achieve. It was a good experience, a bad result, but good things as well. In this level you must be more ruthless."