Barcelona must wait at least another week to wrap up the title after conceding a late goal to draw 2-2 at Athletic Bilbao on Saturday while second-placed Real Madrid won 2-1 at city rivals Atletico.
Victory for Barca at the San Mames and defeat for Real in the Madrid derby at the Calderon would have given the leaders an unassailable 16-point advantage with five La Liga matches left.
Real's comeback win meant Barca's lead was cut to 11 points and the Catalans now have to wait until after their likely elimination from the Champions League at home to Bayern Munich for another chance to secure a fourth Spanish crown in five years.
With an eye on Wednesday's semi-final second leg, when Barca need to overturn a 4-0 deficit against the Germans, coach Tito Vilanova initially left La Liga top scorer Lionel Messi and playmaker Andres Iniesta on the bench.
Bilbao, without a home win in six La Liga games against Barca, took a surprise 27th-minute lead when Aritz Aduriz crossed for Markel Susaeta to finish from close range.
Barca huffed and puffed in search of an equaliser but were fortunate not to fall 2-0 behind when Susaeta struck a free kick against the crossbar 10 minutes into the second half.
Only when Argentina forward Messi, who missed the last three La Liga games with a hamstring strain, came off the bench on the hour did Barca find their cutting edge.
The World Player of the Year brilliantly weaved his way through a crowd of defenders to equalise in the 67th minute and Alexis Sanchez, who earlier struck the post, made it 2-1 two minutes later from a Messi assist.
Messi's goal, his 44th in 33 league matches this season, set another record as it took his tally away from home to 24, one more than the previous best set by Real Madrid forward Cristiano Ronaldo last term.
The Argentine has also scored at least one goal in his last 20 league appearances while Barca equalled their La Liga record by scoring for the 26th consecutive away match.
They looked to have another three points safely in the bag before Bilbao midfielder Ander Herrera rifled a low shot into the corner of the net on 90 minutes to send the home fans into raptures on a wet and chilly evening in the Basque Country.
"The Athletic stadium is a very difficult place to play and you saw that as we had the match won," Barca assistant coach Jordi Roura told a news conference.
"We are closing in on our goal bit by bit."
Real Madrid, 4-1 down to Borussia Dortmund after Wednesday's semi-final first leg, are also facing Champions League elimination and coach Jose Mourinho fielded a second-string side at Atletico.
He was also missing Portuguese compatriot Ronaldo, Real's top La Liga scorer with 31 goals who damaged a thigh muscle at Dortmund.
"The Athletic stadium is a very difficult place to play and you saw that as we had the match won"
Barca assistant coach Jordi Roura
Atletico, who began the game three points behind Real in third spot and seeking their first win in 22 meetings with their city rivals, took the lead in the fourth minute when Colombia striker Radamel Falcao nodded his 26th league goal of the season.
Real were level nine minutes later when Angel Di Maria's inswinging free kick took a slight deflection off defender Juanfran and flew past keeper Thibaut Courtois into the net.
After Real repelled some intense Atletico pressure, Di Maria struck a 63rd-minute winner after running on to Karim Benzema's pass and firing a low shot past Courtois into the far corner.
It was a rare moment of quality in a scrappy game littered with play acting, fouls and yellow cards and was a poor advert for next month's King's Cup final when the two teams will meet at the Bernabeu.
Barca host Real Betis next weekend while Real Madrid take on Real Valladolid.
Also on Saturday, Celta Vigo boosted their chances of avoiding relegation when they won 1-0 at Levante to climb out of the drop zone.
Real Mallorca and Real Zaragoza, second from bottom and bottom respectively, clash in Saturday's late kickoff.