Villarreal's Champions League hopes took a knock after they suffered a disappointing 1-0 defeat to Las Palmas at the Gran Canaria on Friday.
The Yellow Submarine were on the back foot as early as the 10th minute when Kevin-Prince Boateng gave Quique Setien's side the lead, and their task wasn't aided by the dismissal of Victor Ruiz after 19 minutes.
Los Amarillos had lost just twice at home in the league all season, so it was always going to be difficult for the Castellon outfit to break them down.
The hosts had the lion's share of possession and created by far the most chances, taking the lead from their first real foray into the opposition area on 10 minutes.
Dani Castellano sent in a dangerous cross from the left that was headed in by Boateng rather fortuitously off his shoulder.
The team from the Canary Islands were further boosted nine minutes later when Ruiz was shown a straight red card for a poor challenge on Boateng.
Andres Fernandez was kept very busy in the visiting goal as an onslaught ensued, with Mauricio Lemos, Mateo Garcia, Boateng, Roque Mesa and Vicente Gomez all testing the keeper before half-time.
Fran Escriba's men briefly looked to respond after the break, Nicola Sansone and Manu Trigueros drew saves out of Raul Lizoain with their respective shots from distance, but Fernandez was given far more work as the second half progressed.
The on-loan FC Porto gloveman denied Jonathan Viera from inside the area on 69 minutes before keeping out two long-range efforts from Alen Halilovic in the closing stages.