Barcelona dropped points for the third time in their last five La Liga games as they drew 1-1 at struggling Las Palmas.
Ernesto Valverde's team remain unbeaten in their domestic division but now own just a five-point advantage ahead of hosting second-placed Atletico Madrid on Sunday.
They went ahead through Lionel Messi's free kick yet a controversially-awarded penalty, either for Sergi Roberto's tug on Matias Aguirregaray or a Lucas Digne handball, was converted by Jonathan Calleri as Las Palmas claimed a point against Barca for the first time since 2002.
The decision was the first penalty to be whistled against Barcelona in La Liga since February 2016, 79 matches ago.
Messi and Luis Suarez had scored five times between them against Girona at the weekend and should have picked up where they left off in the eighth minute.
It was Messi who won the ball in midfield and drove at the hosts' defence, unselfishly seeking out Suarez with a weak pass that allowed goalkeeper Leandro Chichizola to narrow the angle and make the save.
Chichizola was equal to Messi's first free kick from outside the box as he threw himself across to tip the ball away after the Argentinian had curled it over his wall.
However, the next time Messi had a dead-ball situation, from the same side but a little closer in the 21st minute, he dispatched it into the net.
Ximo Navarro's cynical foul from behind did not force Messi to go down but he won the free kick anyway, and Barca's talisman rifled the ball into the opposite top corner to leave Chichizola with no chance.
The home side's best chance in the first half came with nine minutes to go when a ball over the top had Marc-Andre ter Stegen caught in two minds, with Calleri waiting too long to pull the trigger on a shot that was off target.
Barca were then left furious when Chichizola went unpunished as the ball struck his arm way outside of the area on the stroke of half-time.
The keeper completely missed his sliding clearance as he rushed out before Suarez and the ball clearly hit his arm but referee Antonio Mateu deemed that was not intentional, much to Valverde's annoyance.
His team's mood only worsened when the official surprisingly pointed to the penalty spot early in the second half.
Confusion reigned over the reason for the decision, which came following Alen Halilovic's corner. Aguirregaray appeared to be wrestled by Sergi Roberto and after Suarez inadvertently deflected it onto the woodwork, the ball came back and appeared to graze Digne's arm. It was only then that referee Mateu pointed to the spot and Calleri lifted his chance high into the roof of the net.
Substitute Philippe Coutinho was called for shortly afterwards but a brilliant last-ditch challenge from Aguirregaray prevented Messi from bearing down on goal one-on-one.
Suarez then had two good back-post opportunities, the first of which he fired into a defender and the second he rifled narrowly wide, though Las Palmas' terrific defending was preventing Barca from frequently carving out chances.
Indeed they may have claimed an unlikely winner had Tana not hesitated and allowed Samuel Umtiti to atone for his error and clear when the hosts were in the box.
There were six minutes of stoppage-time yet Barcelona, who had brought on Ivan Rakitic and Ousmane Dembele, could not find a winner.