Football matches nowadays are full of surprises the best teams you expect to win most times are the teams struggling to get a draw that is what happened in the case of Rayo and FC Barcelona in the game Barcelona was already favoured but when the game started everything changed as Rayo was too powerful for them to defeat. Barcelona struggled to control the game they were not in full control and the defense of Rayo made it impossible for them to penetrate but finally Barcelona as awarded a penalty for them to bounce back in the game. Fans should understand that Barcelona will not win all the time and last season is not the new season where they were too strong to be defeated by other opponents this is a new season the unexpected will happen to any bug team that is how the game has always been.
I watched the game between Rayo vallocano vs Barcelona live, I was really disappointed with what I saw in the game because this Rayo vallocano side outplayed Barcelona so much, especially in the second half of the game, and to be frank, Barcelona was very lucky to go home with a single point because it was a game they would have lost 5-1 or 6-1 if Rayo vallocano was not wasteful in front of goal, that's why I really don't see this Barcelona team going very far in the uefa champions league because their defense and midfield is just too weak to withstand a team that knows how to play and keeps the ball but are very physical in midfield, so they really need to improve in those areas because they might not be lucky in snatching a single point next time if they continue with such a performance like that.
I also watched their match live and bet on Barcelona I was almost 100% sure that Barcelona would definitely win against Rayo Vallecano. But I should have thought that sometimes the best teams can lose to weak teams or draw. I shouldn't have been so confident in Barcelona. Whether it was expected or unexpected Rayo Vallecano played great and drew I think it is equivalent to a win for them because to draw with a strong team like Barcelona must have been a result of their best performance.
I agree with you that Barcelona had a high chance of losing this match but they are lucky that they could go home with a point. You can't predict the next matches based on one match they played badly in this match maybe they will do better in the next matches and it is almost certain that they will play more better in the next matches.