02/12/2013 04:34 GMT

Athletic Bilbao 1-0 Barcelona: La Liga Champions' Unbeaten Run Ends (PICTURES)

Barcelona's unbeaten start to the Primera Division was ended on Sunday night, as Athletic Bilbao claimed a deserved 1-0 victory at San Mamés Barria.

Iker Muniain steered home the only goal of the contest 20 minutes from full-time, as Barça slipped to a second loss in five days following their disjointed defeat to Ajax in the Champions League on Tuesday.

While the loss in Europe can be absorbed, defeat in La Liga is much more damaging with Gerardo Martino's men now level with Atlético Madrid at the summit on 40 points, three clear of a Real Madrid side who appear to finally be hitting their stride.

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Nevertheless, Barça midfielder Sergio Busquets is refusing to get overly concerned by their recent results, saying after the Athletic defeat: "There's no need to be alarmed, we just have to carry on.

"We have to win the two (league) games that are left to play this year and learn both from our errors and the things we are doing well."

Photo gallery Athletic Bilbao 1-0 Barcelona See Gallery

Teammate Andrés Iniesta felt his side were relatively comfortable until the goal, saying on his club's website: "We had the game under control, but the goal really hurt us. San Mames is always a tough place to come to.

"We put in a good first half and we played well at times after the break, but the goal really shook us and although we really tried, we couldn't come back."