Espanyol powered into the lead thanks Christian Stuani's strike but though Gonzalo Higuain equalised in the second half, Jose Mourinho's defending champions slipped seven points behind their rivals with only two games left.
Tito Vilanova's side travel to Atletico Madrid on Sunday.
Elsewhere, Athletic Bilbao took a giant step towards sealing their Primera Division status after overcoming nine-man Real Mallorca 2-1 at San Mames.
Aritz Aduriz gave the hosts an early lead but then missed a penalty after Andreu Fontas was sent off on 25 minutes.
Fernando Llorente doubled the advantage late in the second half but Mallorca forward Giovani Dos Santos made for an exciting finish by netting a superb goal two minutes later.
However, Mallorca's hopes of snatching a late equaliser were struck a blow in injury time when Ximo Navarro was also sent off for a second booking and Athletic were able to hold on.
Osasuna also moved closer to survival when Alejandro Arribas struck a second-half winner in their 1-0 victory over Getafe.
Arribas netted 16 minutes from time as Osasuna ended a five-match winless streak with a deserved triumph that moves them four points above third-bottom Deportivo La Coruna, who lost 1-0 at Real Valladolid earlier in the day.
While Saturday's result could help save Osasuna's Primera Division status, it was a blow to Getafe's hopes of getting into Europe next season.
Valladolid are guaranteed top-flight status for another season after their win.
Javi Guerra struck three minutes into the second half to score the only goal of the game and take his team onto 43 points, 11 ahead of the Galicians, who still occupy the final relegation spot.
The game was a tight affair from start to finish, with neither side taking many risks and few openings appearing.
After a first half of no clear chances, the home side made the decisive breakthrough four minutes into the second period.
Patrick Ebert swung in a corner into the six-yard box and Guerra showed great technique to backheel the ball into the net.