Real Madrid failed to take advantage of La Liga leaders' Barcelona's 2-2 draw with Celta Vigo on Saturday as they were held to a goalless draw at Athletic Bilbao, while Atletico Madrid profited by beating Real Sociedad 2-1.
Antoine Griezmann's 88th minute strike saw Atletico complete a comeback after falling behind in the first half to cut their deficit with Barca to six points, while Real stay eight behind Ernesto Valverde's side. Second-placed Valencia can go two points behind Barca, who have 36 after 14 games, if they beat Getafe on Sunday.
Barca also went behind in the early game as Celta striker Iago Aspas silenced the Nou Camp by putting the visitors ahead in the 20th minute. However, goals from Lionel Messi and Luis Suarez either side of halftime put Barca in front.
Celta's Uruguayan striker Maxi Gomez levelled in the 70th minute, capitalising on Barca defender Samuel Umtiti tearing his hamstring as he tried to keep up with the Spanish forward.
Real were up against an Athletic side in crisis, sitting 16th in the standings and reeling from a shock King's Cup defeat to tiny Formentera. But the Basques upped their game with the help of the raucous home support and frustrated the champions, who hit the woodwork twice and had Sergio Ramos sent off.
The Real captain returned to action wearing a protective mask after two weeks out with a broken nose and picked up an early booking for elbowing Raul Garcia. His second came with four minutes remaining for striking Aritz Aduriz, earning a record-extending 19th red card in La Liga.
"Real Madrid are eight points behind Barcelona because we have lacked goals this season," said Real coach Zinedine Zidane. "The biggest change from last season is the results, I don't think we are playing any different. Last season we won games in the last minute and now we can't seem to find the net."
Barca's frustrating afternoon at a cold and sparsely attended Nou Camp was made worse by France international Umtiti being ruled out for eight weeks, including missing the Clasico at champions Real Madrid on Dec. 23.
"The injury cost us the goal, it was an accumulation of catastrophes, because of the draw and the injury," Valverde told a news conference.
"Losing Samuel right now is a big loss, he was in excellent form."
Barca bombarded Celta's area in the remaining 20 minutes after Gomez's equaliser, with Gerard Pique hitting the near post from close range, but could not avoid dropping points for the second game in a row for the first time this campaign.
"We kept trying to win the game and had chances to do that. We have dropped two points but this is nothing that hasn't happened before," Valverde added.
Atletico moved to within six points of Barca thanks to Griezmann's late strike after Filipe Luis had cancelled out Real Sociedad forward Willian Jose's first half penalty in the 63rd.
Griezmann, who came through the academy at Real Sociedad before being sold to Atletico for 25 million euros ($30 million) in 2014, slid in at the far post to nudge in Saul Niguez's header and keep Atletico's title hopes alive, but chose not to celebrate the goal.
"We're happy to have got the job done in a really difficult game which quickly went uphill for us," Atletico coach Diego Simeone said.
"We have to appreciate the pride we showed in the second half, our intensity, insistence and bravery. We now have renewed energy which helped us to take the next step. We missed a lot of chances but we never stopped trying."