Osasuna were beaten for the fourth time in five games as second-half strikes from Hector Moreno and Mubarak Wakaso gave Espanyol all three points at Estadio El Sadar on Sunday.
Mexico international Moreno nodded home Wakaso's corner from close range to break the deadlock on 51 minutes.
Wakaso then made sure of the three points in stoppage time with a stunning long-range effort from a narrow angle.
Espanyol rise one place to 11th in the La Liga table, while Osasuna remain five points clear of the relegation zone in 15th.
