Barcelona threw away a two-goal lead set up by Lionel Messi and Ivan Rakitic in the final 13 minutes as Deportivo la Coruna struck a blow to their title hopes with a 2-2 draw on Saturday.
Despite missing the injured Neymar, the European champions looked on course to bounce back from last weekend's 1-1 draw at Valencia thanks to stunning strikes from Messi and Rakitic.
However, Lucas Perez scored for the sixth consecutive game to bring Deportivo back into the game at the Nou Camp before he set up Alex Bergantinos to fire home an equaliser four minutes from time.
Barca now lead Atletico Madrid by three points at the top of the table, but Diego Simeone's men can move joint top with victory over Athletic Bilbao on Sunday.
Real Madrid, who are two points further adrift of Atletico, travel to Villarreal on Sunday.
With Barcalona not in La Liga action next weekend due to their participation in the Club World Cup, they could fall to third before the end of the month.
“It is little inexplicable. We lost control when we had to have it and we made it easier for them when it was 2-0,” Barca captain Andres Iniesta told Canal Plus. “They are things that happen. We have to analyse it so it doesn't happen again. In two weeks we have lost four points which has closed everything up.”
Barca were without La Liga's top scorer, Neymar, due to a groin injury he picked up in midweek ahead of their Champions League clash with Bayer Leverkusen, and missed the Brazilian's inventiveness against a well-organised Deportivo.
Luis Suarez was looking to score for the ninth consecutive game, but the Uruguayan was unusually wayward when he fired wide a glorious chance from Sandro Ramirez's knockdown early on.
Messi looked back to his best after a few rusty performances on his return from a two-month knee ligament injury and he nearly teed up Andres Iniesta with a sensational through ball that the Spanish international just couldn't stretch to turn home.
The visitors frustrated Barca by denying space in behind and had a great chance to take the lead themselves when Jonathan Rodriguez was played clean through, but Claudio Bravo rushed from his line to make a fine save.
German Lux turned a Messi drive from distance behind, but there was nothing he could do to prevent the four-time World Player of the Year recording his fifth goal in as many games with a stunning free-kick that dipped into the top corner.
Suarez was off target again with a pile-driver just before the break, but it was Deportivo who made the better start to the second-half and Bravo had to be alert to claim Faycal Fajr's attempted chip.
At the other end, Suarez's search for a goal continued as he was flagged offside as he tapped in from Jordi Alba's unselfish cross.
Barca looked to have made the game safe with another stunning strike as Rakitic rifled the ball into the bottom corner from 25 yards for his first league goal of the season.
Deportivo thought they were back in the game when Perez headed home after Cardoso's initial effort had come off the bar, but he was also ruled offside.
However, Perez was not to be denied his 11th goal of the season moments later as he outmuscled Jeremy Mathieu to slot home.
Perez was also key in teeing up the equaliser as his measured pass was blasted into the far corner by Bergantinos to stun the Camp Nou.
In the evening’s other games, Celta Vigo beat Espanyol 1-0 while Granada picked up a 2-1 away win at Levante.
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