Ivan de la Pena came back to haunt former club Barcelona with a double in last night's shock 2-1 victory at the Nou Camp.
A second-half effort from Yaya Toure wasn't enough for Barca as Espanyol held on for a vital three points in their relegation fight.
Barca coach Pep Guardiola saw the defeat as a positive and explained: "Many people have long said that the Liga was won, but this defeat now will touch all of us.
"I'm not worried about the defeat, but as I said, we will have to wake up."
Asked if he fears his players may start to wobble, particularly after Real Madrid's 6-1 hammering of Real Betis, Guardiola added: "I don't know if they will become nervous with the gap reducing."