With Benfica beating Dynamo Kiev at home, Barcelona had to defeat Bayern away.
But already at the break it was 2-0 to the Germans.
First Thomas Müller nodded in his 50th Champions League goal and then Leroy Sané stood for a real dream goal when he shot the ball behind Marc-Andre Ter Stegen from over 20 meters.
Müller is now one of only eight players to have scored 50 goals in the tournament.
The next goal came in the second half when the 18-year-old giant talent Jamal Musiala put 3-0 from close range.
The last time Barcelona did not play in the Champions League play-offs was in the spring of 2004 when they participated in the Uefa Cup.
In the Spanish league, they are in a modest seventh place.
No dream start for the former major player Xavi who took over as coach a month ago.
Now the Europa League playoff awaits Barca, who finished third in the group.
Bayern have at least impressed in the group stage with six straight victories and a goal difference of +19.
It is the best bet in a CL group game of all time, tangent to their own from the 2019/2020 season.