Villarreal slipped to a 1-0 defeat at Girona on Monday in LaLiga, failing to capitalise on Atletico Madrid's loss against leaders Barcelona.
Marcelino Garcia Toral's side, third, were underwhelming and went down to an own goal from Pau Navarro just before the break.
Villarreal are one point ahead of Atletico, fourth, who were beaten 2-1 by the champions on Saturday.
However, with Real Betis trailing Atletico by 12 points with eight matches remaining, both Villarreal and the Rojiblancos have a strong hold on their top-four places for Champions League qualification.
Villarreal defender Renato Veiga and striker Gerard Moreno went to speak to some of their frustrated fans at the end.
"They weren't happy, just like us," Yellow Submarine skipper Moreno told DAZN.
"We didn't manage to get a shot on target, so it's normal they are unhappy."
Girona had the better of the first half, breaking the deadlock in stoppage time.
Navarro accidentally prodded Arnau Martinez's cross into his own net to give the hosts the lead at their Montilivi stadium.
Villarreal failed to threaten consistently in the second half and Girona held on comfortably to move 12th, eight points above the relegation zone.