It's actually Barcelona that were lucky in the match only if Rayo Vallecano players has converted their chances, 7 shots on target and they scored only one goal, they were not clinical. Kudos to Barcelona goalkeeper tough because he saved his team from getting disgraced by a small team. It was a tough game for the Catalans, hopefully they will work on their poor performance in their next game, that I'm sure of.
Can't Barcelona lose a match, sometimes football will favor the weak side. Both teams on the pitch are having eleven players each, among all these players are millions of euros or dollars paid to them in order play and win matches, favorites don't matter always in football, if the weak side are performing well they will get the complete points. Barcelona still have many matches to cover up even if they had lost the match entirely, Barcelona are still a strong competitor against Real Madrid, it has always been all threes ( Real Madrid, Barcelona or Atletico Madrid) winning the La Liga.