If things stay the same way they are right now, i.e. none of the teams gets ahead by more than 3 points, then everything could be decided on 11th May, during the direct game between Barcelona and Real. Barcelona will have a home advantage, which is a big factor, and Barcelona have won the last 3 games against Real, so surely the odds will be on their side.
Just to play with numbers a little bit. Considering the current league position of the remaining opponents of each team:
Barcelona: 14, 13, 6, 18, 8, 7, 20, 2, 15, 5, 4. Average: 10.18
Real: 18, 16, 17, 4, 11, 8, 1, 7, 10, 12. Average 10.4
Looks like Real has a slightly easier job than Barcelona.