Valencia's eight-game unbeaten run came to an end at Rayo Vallecano on Sunday.
Joaquin Larrivey's fifth goal of the season was enough for Rayo to see off Juan Antonio Pizzi's side, who ended the match with 10 men.
Larrivey broke the deadlock just after the hour mark, heading home from six yards following a pinpoint cross from Razvan Rat.
Rayo were positive and threatened to score a second. Alejandro Galvez's long-range effort forced a good save out of Valencia goalkeeper Diego Alves.
Valencia's hopes of getting back into the game were dealt a heavy blow with 14 minutes remaining when defender Antonio Barragan picked up his second yellow card of the night for a foul on Alberto Bueno.
Nevertheless, two late headed chances fell to Los Che midfielder Sofiane Feghouli, who failed to find the target with either.
The result brings Rayo to within three points of safety, while Valencia stay ninth in the table.
