Javier Aguirre's side looked far more determined than their opponents for the majority of the 90 minutes, suffocating them with high pressing which led to three of their four goals.
Sergio Garcia got the ball rolling by scoring a penalty after five minutes and Christian Stuani doubled the lead half an hour later. Victor Sanchez made sure of the points with a third goal on 67 minutes, and Stuani got his second and the fourth of the day shortly afterwards.
With the three points in the bag the hosts began to relax, and Javi Guerra and Victor Perez each pulled goals back late on for Valladolid, but there was never any doubt as to how the match would end.
It was the Catalans' first win at home in four matches and takes them up to ninth place in the Primera Division while Juan Ignacio Martinez's men are still teetering on the edge of the relegation zone, just one point off the bottom three with their nearest rivals Osasuna and Rayo Vallecano still to play later this weekend.
Espanyol pressed their opponents from the start and won a penalty with less than four minutes played. Jesus Rueda tripped Stuani just as he entered the area, and Garcia rammed the ball home from the spot to score his seventh goal of the season.
The hosts continued to hold the initiative after taking the lead, Stuani testing Diego Marino from long range before the goalkeeper had to make an even better save from a more powerful shot from Sanchez.
It was to little surprise when the Catalans scored again. Fausto Rossi was dispossessed by Sanchez near the Valladolid box and Garcia threaded the ball to Stuani, who side-footed into the opposite corner.
Oscar Gonzalez should have reduced the deficit five minutes before the break, but was thwarted by the legs of Espanyol goalkeeper Kiko Casilla.
The game followed a similar script in the second half, with Garcia squandering two chances to score a third, although Casilla had to make a fine save to deny Guerra.
But midway through the second half the third goal arrived, and Sanchez got the goal his tireless performance had merited.
This time it was Alex Fernandez responsible for the high pressing, the Real Madrid academy graduate robbing the ball on the edge of the area, entering the box and then pulling the ball back for Sanchez to strike into the top corner.
And Fernandez and Sanchez combined again for the fourth goal, Fernandez winning the ball back and releasing Sanchez down the left, the midfielder squaring for Stuani to bundle the ball home.
With 15 minutes remaining Guerra got a consolation goal for the visitors, heading in his fifth goal in three matches and his 11th of the season in the league, and in the last minute of normal time Victor Perez's deflected free-kick went beyond Casilla and into the net.