Valencia suffered a 1-0 defeat at home to Osasuna on Sunday to leave title favorites Real Madrid with a two-point lead at the top of the table.
Third-placed Deportivo Coruna also missed the chance to press their title claims as they went down 1-0 away to Athletic Bilbao.
Valencia, needing to win to reclaim the lead after Real's 2-1 victory over Villarreal on Saturday, had themselves to blame as centerback Mauricio Pellegrino scored a ridiculous own-goal at the end of the first half.
Valencia created several good chances early in the second half but their form soon dipped again and the game finished on an ugly note when Italian defender Amedeo Carboni was sent off for stamping on Osasuna's Pablo Garcia.
The result completed a miserable week's work for Valencia, who went down 3-0 to Real Madrid in the opening leg of their King's Cup quarter-final tie at the Bernabeu on Wednesday.
With 21 games played, Real have 46 points to Valencia's 44, with Deportivo staying third on 40 points after their defeat in Bilbao.
Deportivo, looking to close to within three points of Real, went a goal down early in the second half when Francisco Yeste's long-range strike beat Jose Molina. Javier Irureta's side were well below their best form and rarely threatened a comeback.
Osasuna's surprise win over Valencia took them up to fifth, above Villarreal on goal difference and within sight of Atletico Madrid in the fourth and final Champions League qualification spot.
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