The Bavarians outclassed their Catalan opponents in a manner rarely seen, and with a four-goal advantage to take into the second leg, are surely favorites for a Wembley place.
On the same day that they stunned the football world by capturing Mario Gotze from Bundesliga rival Borussia Dortmund, the Bavarian giants again reminded everyone that they are a force to be reckoned with by playing the Blaugrana off the pitch.
Thomas Muller opened the scoring with a close-range header, and put the second on a plate for Mario Gomez minutes into the second half.
Muller would controversially play a role in Arjen Robben's goal after appearing to foul Jordi Alba off the ball, before tapping in the fourth himself with eight minutes remaining to round off the biggest ever margin of victory in a Champions League semifinal.
Mario Gomez replaced the suspended Mario Mandzukic up front for the hosts, while for the visitors, Marc Bartra partnered Gerard Pique in defense with Carles Puyol and Javier Mascherano injured.
Bayern could have been ahead as early as the fourth minute. Robben exchanged passes with Gomez, and it took the outstretched legs of Victor Valdes to deny the Dutch winger from point-blank range.
Barca was winning the possession battle, but it was the Bavarian side who controlled the opening exchanges. Javi Martinez’ tumble in the box was correctly ignored by the referee, who was forced into a bigger no-call when Philipp Lahm’s shot struck Pique’s elbow.
The Barca defender headed wide at the other end from a corner, but it was an isolated scare from the blunted Catalans, and with 25 minutes on the clock, Bayern made their superiority count.
A corner was worked to Robben, whose cross was flicked on by Dante, and Muller was first to the ball, sneaking a header past Valdes at the post.
Dante had to be alert to prevent a quick response from Barca, poking away Dani Alves’ cross at full stretch from the unmarked Messi, in a dangerous position where an own-goal could have easily occurred.
Gomez then picked up the first yellow card of the game for barging into Messi, and he was quickly followed into the book by Bartra and Martinez for challenges on Muller and Andres Iniesta either side of the interval.
Any hopes that Barca had for the halftime break to revitalize them were dashed only four minutes after the restart, when Bayern exposed the soft center once again to go two goals ahead. Just like the first goal, Robben’s delivery was met by a Bayern head, with Muller guiding the ball towards the goal line, where Gomez was waiting to gleefully bundle the ball home.
The Bundesliga side was simply dominating, and the match threatened to get ugly very fast for Barca had Muller and Franck Ribery been more accurate when presented with the chance to pick their spot from great shooting positions.
The third goal was always in the cards, and it duly arrived with 17 minutes remaining, albeit in contentious circumstances. Muller’s off-the-ball block on Alba went unheeded, and with the fullback out of the way, Robben curled sublimely into the far corner.
Bayern got its fourth in the 82nd minute. David Alaba’s overlapping run down the left ended with a low cross into the six-yard area, where Muller was waiting to turn into the back of the net to leave the second leg at Camp Nou as little more than a formality, and finish off an epic 24 hours for Bayern.