I don't think Barcelona will allow any team to reduce their points in the remaining matches, because their coach has worked on some areas that is not making them to achieve goals on time. Rayo vallecano really prepared to battle with Barcelona in that match, because the match make Barcelona to look as if they are not complete in the field based on the injury that was affecting one of their defender at the moment that gave Rayo vallecano the opportunity to defeated them. I think, there is a hope in that match because Barcelona know how to use home advantage to reduce the strength of their opponent so that it will be easy for them to gain access to their goalpost to embrace victory at the end of the match.
However, we also have to look at the quality and performance of the current Barcelona team realistically, Barcelona has not played well in the last few matches and there are many things that Xavi must immediately fix to make this team much more solid.
I would not be surprised if Barcelona's next match will reap bad results because in my opinion the current Barcelona team is not very strong, especially their bottom line which has conceded a lot this season, especially in the last 2 matches Barcelona conceded 4 goals, that's not a good thing.
And also Xavi's team is currently not well organized, so if they meet tough opponents, I doubt Barcelona will be able to win, but again, if it's still early in the season, anything is possible.