Barcelona's bid for a fifth La Liga title in six years suffered a surprise setback when they crashed to a 1-0 defeat at lowly Real Valladolid on Saturday and opened the door for Real Madrid to pull away at the top.
It was one of Barca's worst performances of the season, particularly during a woeful first half when Fausto Rossi scored for the home side, and the champions squandered a chance to move two points clear of Real at the top.
Real, who host Barca for the 'Clasico' in two weeks, can stretch their lead over their arch rivals to four points with a win at home to Levante on Sunday, while Atletico Madrid will climb above Barca and draw level on 64 points with Real if they beat Celta Vigo later on Saturday.
Barca's players, most of whom were in international action midweek, looked jaded and short on inspiration and Lionel Messi and Neymar wasted a host of opportunities in a lethargic display marked by uncharacteristic sloppiness.
"We failed to create going forward, in our passing and in our mobility and that's why we did not get the desired result," coach Gerardo Martino said at a news conference.
"We are finding it hard to put together a complete game in every aspect of play, a perfect game," added the Argentine, who is in his first term in charge after taking over from the ailing Tito Vilanova.
"As long as we still have a chance mathematically we will keep fighting for the league."
The first genuine chance of the match at Valladolid's Jose Zorrilla stadium fell to Messi when he sprinted into space on the left in the 10th minute.
It was the kind of opening the four-times World Player of the Year normally converts with a minimum of fuss but his rising shot was straight at Diego Marino and the home goalkeeper was able to palm the ball to safety.
Valladolid grabbed the lead seven minutes later when Rossi was first to a loose ball in Barca's penalty area and the Italian fired a first-time effort past Victor Valdes.
Messi and Fabregas again shot straight at Merino when well placed and Messi had another chance early in the second half before Neymar, who netted a hat-trick for Brazil against South Africa on Wednesday, fluffed Barca's best chance of the game.
The ball fell kindly for him in space on the left of the area but his wild shot flew over the crossbar into the stands, prompting derisive whistles from the home fans.
Martino brought Alexis Sanchez on for Fabregas and later switched to what was effectively a two-man defence of Javier Mascherano and Sergio Busquets but Valladolid held firm and came close to another goal on the breakaway late on.
Barca's latest setback follows last month's defeats at home to Valencia and away at Real Sociedad and will give Manchester City hope they can overturn a 2-0 deficit in Wednesday's Champions League last 16, second leg at the Nou Camp.
"We cannot draw any positive conclusions, we just have to try and improve before Wednesday," Barca playmaker Xavi told reporters.
"It's a very painful defeat, a step backwards, but we have to turn things around before the Champions League."
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