After going behind early on, Barca took charge and equalised through Perez just before the break.
Abel Ruiz, who played a key role in the equaliser, doubled Barca's advantage early in the second half, nipping in to score after Busquets’ header crashed off the bar.
Soon after, Jordi Mboule broke through to flick the ball on to Lee to tap home the third.
Mboula saved the best until last as he collected the ball from the halfway line before slaloming his way through the Dortmund defence to complete the scoring.
While Barcelona's senior team might be going through a rough patch, their La Masia Academy junior teams, look like they are playing some really good football.
Barca's official YouTube channel brings us the best goals from the U-12's, U-10's and U-16 matches, that took place this weekend.
Watch out, for there are stunning free-kicks, dribbles, a few belters and tap-ins and a sublime long-range shot.
Andres Iniesta has been a dominant player in Barcelona's midfield over the years. From important goals and assists to spectacular dribbles on the pitch, he is a club legend and renowned as one of the greatest players of his generation.
And this weekend, against Leganes, Iniesta made his 400th league appearance, a record in itself.
In tribute to his La Liga service with Barcelona, the club released this compilation that takes you through his league career for Barca, ever since he made his debut.