The thing is that you don't look down on little things and this is in the case of Barcelona because last season was terrible for them, and their is no way that we are going to be to compare the both of them now the way at which Barcelona is going they are the potential winners because who else do you have confidence in, that you think they will be able to win if not bacelona and I actually love the way they decided to pickup, and even if I love Madrid Barcelona gave them a good season at least next season they will be able to prepare better because their is no way that you won't notice that Madrid is struggling and the best team now in the premier league is not more than Barcelona.
It happened not because Barcelona underestimated their opponents but there were other factors such as fatigue due to the tight schedule of matches in several competitions. This is common and maybe also experienced by other teams because it is impossible for a team to defend consistently and not be defeated. The defeat can also be said that the opponent was more able to maximize the small chances and they really defended with a much more solid formation.
Although some people think that the referee had a little problem in that match, I saw that the opponent was much more able to maximize the opportunities that existed. The competition will probably increase because after this defeat Barcelona will be much more careful and Real Madrid themselves will also try to play more consistently.