In the second week of La Liga Barcelona will visit Real Sociedad, and statistically Real Sociedad is better than Rayo.
I think Real Sociedad will play more openly than defend against Barcelona. From head to head statistics Barcelona always win against Real Sociedad either at home or away.
I also feel confident, in the second match Barcelona will get a perfect win.
However, bookmakers estimate the probability of Barcelona winning as 2.1, which is less than 50% (approximately 45%). Therefore, if you are sure that Barcelona will win, then this outcome will be a value bet for you. I won't bet on this match (maybe I'll do it later live), but Real Sociedad or draw with odds of 1.67 looks more interesting.
In this case, we see the odds are indeed quite interesting from Barcelona, although in their current performance it seems that the bookies are still a little unsure there but indeed this is still a good thing.
I might take a risk even though in this case Real Sociedad are also very good in form especially against some big clubs and being the underdog last season I would probably be at Barcelona's side.