
Valencia had Spain forwards David Villa and Joaquin Sanchez sent off, the former for diving in the penalty area, the latter for insulting the linesman.
Danish veteran Jon Dahl Tomasson gave Villarreal an early lead. Debutant Giuseppe Rossi added a second from the penalty spot, Santi Cazorla completed the rout late on, with Valencia in tatters.
Referee Miguel Perez Lasa needed a police escort to protect him from the angry Valencia fans.
In Sunday's other late match, newly-promoted Valladolid won 1-0 away to UEFA Cup finalists Espanyol thanks to a solitary goal from youngster Joseba Llorente.
This means that all three promoted teams won their opening matches. Earlier on Sunday Almeria had won 3-0 in La Coruna, on Saturday Valladolid had beaten Zaragoza 2-1 at home.
The big news on Sunday was that Barcelona were held to a 0-0 draw by dogged Santader, who played most of the second half with ten men after Ebi Smolarek had been sent off.
Big signing Thierry Henry - who came off the bench with half an hour left - almost broke the deadlock in the 85th minute but his shot hit the Santander post.
In Sunday's other games, Athletic Bilbao were held 0-0 by Osasuna, whilst Betis fought out a 1-1 draw in Huelvaand Mallorca thrashed Levante 3-0.
DPA