Late goals from Fabian Orellana and Nolito handed Celta an unlikely victory in the Primera Division clash, but the encounter will be remembered for the reckless actions of a fan which led to the referee suspending play for over 20 minutes.
Orellana had just headed Celta into the lead when a smoke bomb was thrown on to the pitch, forcing the referee to take the players from the pitch and leading to most of the supporters leaving the stands.
It led to a lengthy stoppage - and considerable confusion as at one stage it seemed the match would not continue - but eventually the players re-emerged and the four remaining minutes were played, enough time for Nolito to add a second.
Defeat dealt a serious blow to the Yellow Submarine's hopes of Champions League qualification and Marcelino, in quotes reported on the Marca website, said: "This experience has been crap, pardon the expression.
"There are attitudes that sometimes humans do not understand and this is one of them. The most positive thing is not to discuss this issue."
Villarreal president Fernando Roig condemned the action and apologised on behalf of the club.
He said: "Villarreal deplores and condemns what happened. We are convinced that this is a person who is outside of Villarreal and has specifically come to harm the club.
"We are making all appropriate inquiries and hope to be able to identify as soon as possible to the perpetrator and come down on him with the full weight of the law.
"Such acts do not represent the fans of Villarreal. The club wants to apologise and to acknowledge the work of the security forces in the evacuation."