Real Sociedad stumbled to a 1-1 draw at Real Mallorca on Sunday in La Liga, with their bid to finish in the top four losing steam at an alarming rate.
Struggling Sevilla earned an important 2-1 win over Almeria to climb to 13th, two points clear of the relegation zone, leaving their opponents 19th.
Real Sociedad have just one win in their last nine matches across all competitions and were frustrated by hosts Mallorca, 10th.
The Basque side remain fourth, level on 45 points with third-place Atletico Madrid, who visit Girona on Monday.
Real Sociedad captain Mikel Merino was dismissed late on for a late lunge on Abdon Prats to make a disappointing afternoon worse still.
Beaten in the Europa League last 16 first leg by Jose Mourinho's Roma, Real Sociedad were trying to bounce back with their first league win in four games.
Carlos Fernandez fired the Basque side ahead after just three minutes with a well-taken strike.
Veteran playmaker David Silva fed the forward, who drilled into the bottom corner.
Real Sociedad dominated the first half but could not extend their lead, and soon paid the price.
Lee Kang-In levelled for Mallorca after defender Jon Pacheco stumbled, with the South Korean forward slipping in behind and finishing well.
Merino was sent off for a dangerous lunge on Prats after losing the ball with a poor touch, in the final stages.
"Today we wanted to win and the team's reaction after their goal was phenomenal," said Real Sociedad coach Imanol Alguacil.
"Being close (to winning), it escaped us, and we can do nothing else but reset and try to improve."
Real Betis, fifth, are four points behind La Real and face sixth-place Villarreal later Sunday, before leaders Barcelona visit Athletic Bilbao.
Lamela lifeline
Jorge Sampaoli made five changes to the Sevilla side which beat Fenerbahce in the Europa League on Thursday to try and freshen up his side, but Almeria took an early lead.
Sergio Akieme finished well from Alejandro Pozo's cross to silence the Ramon Sanchez-Pizjuan -- a terrible start for Sevilla, who began the day in the relegation zone.
The goalscorer soon went off injured, along with Almeria striker El Bilal Toure, while Sevilla goalkeeper Yassine Bounou also suffered an injury and had to be replaced.
The Morocco international collided with team-mate Alex Telles and was taken off on a stretcher with Marko Dmitrovic replacing him.
Bounou went hospital for precaution and will undergo tests, Sevilla said on Twitter.
The hosts levelled towards the end of the first half, with Lucas Ocampos slotting home a penalty after Telles was felled.
Lamela headed home winger Bryan Gil's cross to send Sevilla ahead after 73 minutes.
Youssef En-Nesyri should have wrapped up the win when through on goal but rolled a tame effort into the side netting after taking it past Fernando Martinez.
Sevilla held on, bouncing back from their 6-1 humiliation by Atletico Madrid last weekend to clinch three vital points.
