Barcelona's title defence took a blow when it stumbled to a 1-0 defeat at Valladolid, missing the chance to move top of the Spanish standings on Saturday ahead of its Champions League clash with Manchester City at Camp Nou.
Atletico Madrid took advantage of Barcelona's latest slip by winning 2-0 at Celta Vigo courtesy of David Villa's two goals in a three-minute span to move ahead of Barcelona and level on points with Real Madrid at the top of the standings.
Once the league pacesetter, Barcelona has won just two of its last seven away league games and trails its title rivals by one point before Madrid hosts Levante on Sunday.
Lionel Messi was the only Barcelona player who looked sharp, while his teammates were plagued by uncharacteristic passing errors and again proved brittle at the back.
Valladolid outplayed the defending champions early and midfielder Fausto Rossi netted the winner in the 17th minute. The relegation-threatened side then did well to protect three points against the star-studded visitors for the remainder.
After its strong start this season under first-year coach Gerardo Martino, Barcelona has dropped points in five of the last nine rounds.
"As long as it is mathematically possible we will keep fighting," said Martino, whose team visits Madrid in two weeks. "We are not in our best form, and we have to rediscover it within 15 days. We are worried because the league title is being decided right now."
Man City next
Before the clasico, however, Martino will have to regroup his team against City on Wednesday. Barcelona will be looking to protect its 2-0 lead in the second leg of their Champions League last-16 tie.
Valladolid started the round in the drop zone, but the big win — only its fifth in 27 league games this season — provisionally pulled it out of danger.
"It's an incredible result," said Rossi, who was at Valladolid on loan from Juventus. "All together we can save this team."
Also, last-place Real Betis gave a boost to its slim hopes of staying up by beating Getafe 2-0 in Seville.
Betis won thanks to first-half goals from forwards Leo Baptistao and Ruben Castro to keep the hapless Getafe winless in 12 consecutive rounds and only one point from relegation.
After Barcelona lost 3-1 at Real Sociedad in its last league away match, Martino aligned his best 11 available without Andres Iniesta, who didn't travel with the team for undisclosed personal reasons.
Even so, Barcelona lacked its regular cool composure from the start and failed to dominate possession until it was trailing in the score. Holding midfielder Sergio Busquets, usually so sure with the ball, erred on three passes before the 25-minute mark.
By that time Valladolid had threatened Barcelona's area and taken the lead when Rossi finished off a rebound after both his first attempt and Javi Guerra's follow-up had hit defenders.
Messi's solo effort saved by goalkeeper Diego Marino in the 10th was all the visitors could muster in the first half hour. Barcelona then improved and Messi and Cesc Fabregas forced Marino to make three more saves before halftime.
Messi, who showed no signs of his apparent vomiting from Argentina's 0-0 draw against Romania this week, used a burst of speed to break free in the 48th, only to be denied again by Marino.
Messi got little help. Neymar had a quiet match and sailed his only scoring chance over the bar before he was substituted.
Atletico was without leading scorer Diego Costa, playmaker Arda Turan and centerback Diego Godin, all three due to suspension.
That meant Villa, who was recently dropped from Spain's squad for its friendly with Italy, got the nod up front. And after a dull first half, the former Barcelona striker notched his 12th and 13th league goals of the campaign.
Villa first pounced on a poor pass by Celta's Jonathan Castro, dodged Andreu Fontas' last-ditch tackle, and drilled the ball beyond goalkeeper Yoel Rodriguez in the 62nd. He slotted in his second goal to seal the victory two minutes later.
Atletico hosts AC Milan on Tuesday in the last-16 of the Champions League after winning 1-0 in their first meeting.