Real Madrid suffered their third league loss of the Primera Division season after going down 1-0 at Villarreal.
Roberto Soldado's ninth-minute, close-range goal proved enough to secure victory on an evening when Rafael Benitez's team disappointed with their lack of a consistent goal-threat against their well-organised hosts.
The result will again increase the pressure on Benitez, whose third-placed side now trail joint La Liga leaders Barcelona and Atletico Madrid by five points, and again prompt questions about their discipline and inconsistency, particularly given their previous fixture was an 8-0 win over Malmo in the Champions League.
Villarreal, who were perhaps fortunate not to win by a more convincing scoreline after bossing the first half, remain fifth, but trail fourth-placed Celta Vigo by only a point.
Jonathan Dos Santos had already struck the post for Villarreal when Soldado gave them the lead. The latter left Tottenham, where he is regarded as a huge disappointment for the £26 million they paid for him, in the summer to return to Spain, where he is rightly remembered as a frees-coring striker, and converted the sort of opportunity on which he typically thrives.
Luka Modric was dispossessed in midfield by Bruno Soriano, who in turn passed to Cedric Bakambu, whose square pass to Soldado, after driving forward, was impressively finished by the striker between goalkeeper Keylor Navas' legs.
It took until early in the second half for Real, who again started with their all-star attacking trio of Cristiano Ronaldo, Karim Benzema and Gareth Bale, to truly threaten.
After Bale had played him in behind Villarreal's defence, Benzema controlled possession before sending a half-volley just beyond the post.
Almost immediately after, the striker then missed a superior goalscoring opportunity. Bale hit the byline before sending a cross towards the near post, and though Benzema found space he again missed the target when a player of his quality should have scored.
Real continued to dominate possession thereafter, but Villarreal gradually adjusted, and midway through the second half again began to frustrate their decorated opponents.
Benzema's next chance came in the 74th minute, this time from an equally dangerous cross from Ronaldo. Unmarked, the Frenchman read Ronaldo's ball and met it with a header but, with goalkeeper Alphonse Areola apparently beaten, his effort went wide of the left post.
James Rodriguez came close late on, when during an otherwise-quiet performance he ran down the right, cut inside on his left foot and shot just wide of the right post, but with his miss Real's defeat was effectively secured.