Goals from Thomas Mueller (2), Mario Gomez and Arjen Robben have left Lionel Messi and his teammates with the proverbial mountain to climb at Camp Nou in the second leg.
However, if Bayern are considering any complacency for the return match, they should start looking to recent history for a warning sign.
When Barcelona last played host to a German club in the Champions League, they produced a clinical demolition of Bayer Leverkusen.
Barcelona were already leading 3-1 from the last 16 first leg when the Bundesliga team arrived, but the eventual 10-2 aggregate score was a stunning statement of intent a year ago.
Messi became the first man to score five times in one match in the Champions League, taking his tally to 53 goals in 49 games for club and country at that point.
Cristian Tello came off the bench to replace Andres Iniesta and struck twice, while Leverkusen substitute Karim Bellarabi grabbed the scantest of consolations in injury time.
True, Bayern are a far different team to their Leverkusen counterparts from last season, with a current run of 14 successive Bundesliga wins while the title was clinched several weeks ago.
But Barcelona remain a team indelibly linked with the Champions League, and they will not cede ground in UEFA's elite tournament without a fierce battle.
Messi came off the bench at Athletic Bilbao to ignite Barca's fightback before a late equaliser earned the home side a point in a 2-2 draw.
Importantly, the Barcelona players believe they can still turn around the four-goal deficit against Bayern. The Guardian reports Gerard Pique's opinions on the task ahead of La Blaugrana:
After a 4-0 result you do doubt yourself but, as days go on, you suddenly believe you can do it. We represent a club that does not consider giving up, a club that has won a lot and has a long history. We represent FC Barcelona and we will want to give a good image. We believe we will turn this around, 100 percent
Bayern coach Jupp Heynckes has a dilemma ahead of the second leg with Javi Martinez, Mario Gomez, Bastian Schweinsteiger, Luiz Gustavo, Dante and Philipp Lahm all one booking away from missing the final.
Such a factor could work in Barcelona's favour from a psychological viewpoint, even though the La Liga side are likely to field Marc Bartra alongside Gerard Pique in an experimental central defence in place of the suspended Jordi Alba.