I don't think Rayo Vallecano is a team that can fight for the title. Rayo Vallecano however managed to share the points with Barcelona. But their performance was not as good as expected. In the whole match they only resisted attacks from Barcelona players. They managed only 4 shots in 90 minutes. I don't think such a team will fight for the title. The battle for the title this season will be between Barcelona, Real Madrid and Atletico Madrid.
Agree about this most chances they will try their best for staying into top six teams despite fighting for title race because it's start of the season and just after two matches we can't judge any team for title race specially when we have giants like Real Madrid, Barcelona and Atlético Madrid for title race and Villarreal, Read Sociedad and Sevilla are fighting hard for fourth spot.
Most of the things could be clear after winter break because then we can predict better about title race as we will have half of the season and most of the teams could be in better shape for their chances and players will be also having in good touch with their performance right now predicting about any result is surely not possible specially just after two matches.