Barcelona conceded a second goal to Getafe forward Angel Lafita in injury time to stumble to a deflating 2-2 draw at home on Saturday, dealing a major blow to its hopes of repeating as Spanish league champion.
Lionel Messi volleyed in Dani Alves's pass for his 28th league goal this season in the 23rd minute, only for Lafita to level after a rare attack for Getafe in the 37th.
Substitute Cesc Fabregas appeared to put Barcelona back on track when he initiated a move that ended with Alexis Sanchez scoring in the 67th.
But Barcelona's brittle defence again betrayed it in the final moments when Lafita charged in to head home Jaime Gavilan's cross and grab a draw that silenced the Camp Nou.
Out of the Champions League and Copa del Rey, Barcelona's chances of defending its domestic crown are fading fast. The Catalan club was left three points behind Atletico Madrid before the leader visits Levante on Sunday.
There are two more rounds after this weekend. Real Madrid trails Atletico by six points but has a game in hand. Despite still being mathematically alive, Barcelona appears to have given up the title.
"This hasn't been a good season, nor is this the way we wanted it to end," Barcelona coach Gerardo Martino said. "The responsibility lies with the manager. Our expectation was to stay in it as long as we could. We did so until today. If we haven't been able to beat a team fighting to stay up, then we don't deserve to be champions."
Barcelona has been sub-par in the second half of the season. After dropping just four points through the first 18 league games under Martino, it has dropped 18 points in the last 18 rounds.
Martino, who is widely expected to be fired, added, "Sometimes you don't think it's necessary to ask for a second chance because you don't deserve one."
Elsewhere, Celta Vigo won 2-0 at Osasuna, Elche won 1-0 at Malaga, and Valladolid edged Espanyol 1-0 as it tries to escape the relegation zone.
Barcelona's first home game since former coach Tito Vilanova's death last week from throat cancer featured a commemorative video, an enormous banner with the message "Tito, Always Eternal," and a minute's silence before kickoff.
Barring slipups by Atletico and Madrid, Barcelona won't win a major title for the first time since the 2007-08 season, before former coach Pep Guardiola took over with Vilanova as his assistant. Vilanova led the team to the league title last year in his only season as coach.
Barcelona dominated the outclassed Getafe for the first 80 minutes, but its lack of scoring touch cost the host dearly.
Lafita converted two of Getafe's three scoring opportunities, while Pedro Rodriguez and Alexis were particularly off target for a Barcelona side that generated a plethora of empty shots.
Barcelona midfielder Sergio Busquets said the players were the "only ones" to blame.
"We have committed mistakes that are not befitting players who want to play in this league. We won't win any titles this year, and I hope that serves the team in years to come."
Getafe rested one point above the relegation zone.
In Pamplona, Manuel "Nolito" Agudo scored his third brace in as many games for Celta. He struck first in the 20th with an exquisite chip shot and followed that by driving in a cross from an angle in the 34th.
Celta climbed into eighth place while Osasuna was left level on points with Valladolid and clinging to safety.
Elche moved four points above the drop after winning at Malaga thanks to Garry Rodrigues' goal in the 11th.
Elche had two players shown direct red cards. Reserve goalkeeper Antonio Rodriguez was booked for coming off the bench to argue with Malaga's players in the 68th, and defender Alberto Botia was sent off in the 82nd for kicking the ball into a prone Malaga player after a foul.
Valladolid defender Antonio Rukavina scored in the 20th and Espanyol was never able to mount a comeback, with Luis "Pizzi" Afonso dismissed with a second yellow card in the 72nd.
Valladolid striker Manucho injured his leg in the second half and had to carted off.