Espanyol extended Villarreal's winless streak to six games in all competitions as two goals from Felipe Caicedo handed the Catalans a 3-0 win at El Madrigal.
Caicedo had a slice of fortune in opening the scoring as Javi Lopez's miscued header deflected off the Ecuadorian and he then he thumped home his second of the evening after the break at Sergio Asenjo's near post.
Asenjo had a night to forget as he also spilled Sergio Garcia's cross 11 minutes from time to allow Victor Sanchez to roll the ball into an empty net to complete Villarreal's misery.
This defeat leaves Villarreal still just five points ahead of Malaga in the final Europa League spot in sixth, whilst Espanyol moved up to ninth.
Villarreal's season has unravelled in recent weeks with elimination from the Copa del Rey and the Europa League, but a hard-earned 0-0 draw away to Valencia at the weekend had raised hopes they could end the league campaign on a high note.
However, there was little encouragement for Marcelino Garcia Toral's men in this display as they slumped to a fourth defeat in six games in all competitions.
The opener arrived on 24 minutes as Real Madrid loanee Lucas Vazquez fired in a dipping free-kick that caught Asenjo unaware and after the ball came back off the bar, Caicedo was on hand to divert Lopez's headed effort into the net.
Asenjo's consistent performances this season had seen him called up to the Spain squad last month, but his horror show continued 22 minutes from time as Caicedo spun his marker on the edge of the area and his shot had too much power on it for the former Atletico Madrid custodian at his near post.
And Sanchez rounded off Espanyol's first away win in nearly two months 11 minutes later with the easiest of finishes after Asenjo had dropped Garcia's cross at his feet just inside the area.