Atletico Madrid's poor week following Champions League defeat by Chelsea continued as they lost more ground in the La Liga title race in a 0-0 draw at modest Madrid neighbours Leganes on Saturday.
Oblak saves Atlético from Liga loss
But for a brilliant second-half save from Jan Oblak to deny Nabil El Zhar, Leganes could even have registered their first ever win over Atletico in the top flight.
A third draw in seven games this season sees Atletico fall a point behind Sevilla, who moved up to second earlier with a 2-0 win over Malaga.
Barca can extend their lead at the top to five points with victory at home to Las Palmas on Sunday. Real Madrid are also in action on Sunday when they host Espanyol.
Atletico boss Diego Simeone made four changes from the team that started against Chelsea in an attempt to refresh his side.
However, the visitors still looked leaden-footed and confused by a change of system to three at the back.
Leganés prove a match for the big boys from Madrid
Leganes also had the best chance of the first half when Claudio Beauvue fired inches wide.
At the other end Leganes 'keeper Ivan Cuellar just had one stop to make before the break when he parried Saul Niguez's fiercely struck drive from the edge of the area.
El Zhar was introduced at the break and quickly stung the palms of Oblak.
However, it took a sensational one-handed stop from the Slovenian on the hour mark to turn El Zhar's next effort over for a corner.
Despite Atletico's lack of cutting edge in the final third, Simeone took the strange decision to replace top scorer Antoine Griezmann with full-back Sime Vrsaljko 25 minutes from time.
Without the Frenchman the best Atletico could muster was a Diego Godin header that Cuellar comfortably turned behind.
A point continues Leganes' fine start to the season as they move level with Real Madrid on 11 points in sixth.
By contrast, a sixth defeat in seven games pushes Malaga boss and legendary former Real Madrid player Michel ever closer to becoming already the fourth managerial change of the La Liga season.
Sevilla had to wait until 22 minutes from time to open the scoring from the penalty spot at the Sanchez Pizjuan and with some fortune when Roberto Rosales was harshly adjudged to have brought down Joaquin Correa inside the box.
Ever Banega coolly dispatched the spot-kick and just two minutes later Luis Muriel showed great pace to burst clear from the halfway line into the Malaga box before firing inside Roberto's near post.
Alaves ended a run of six defeats to start the season with a 2-0 win at Levante thanks to goals from Munir El Haddadi and Alvaro Medran.
And former West Bromwich Albion manager Pepe Mel's job at Deportivo la Coruna was saved by a second-half fightback to beat Getafe 2-1.
Amath Ndiaye put the visitors in front at La Riazor, but Lucas Perez levelled with his first goal since returning to the club on loan from Arsenal before Florin Andone grabbed the winner three minutes from time.