David Villa's goal just after half-time was enough to see off Sporting Gijon as Barcelona lumbered through 1-0 with another lethargic display in front of their home fans.
Away manager Manolo Preciado made eight changes and while Barcelona were without their star man Lionel Messi they would have expected a far easier evening when the team sheets were announced.
Sporting's fringe players proved, however, a resilient match for Barcelona who dominated possession but had to rely on Villa's 49th-minute strike after Dani Alves' through-ball gave him a rare sight of goal.
The last remaining 100% record in La Liga came to an end after Valencia were held to a 1-1 draw by Atletico Madrid at the Mestalla. However, it could have been worse for Los Che as they needed a late equaliser from Aritz Aduriz to salvage a point after Atletico had taken an early lead through Simao Sabrosa.
The result means Valencia move level on 10 points with leaders Real Madrid while Atletico, who saw their own perfect start to the season ended by a 2-1 defeat to Barcelona on Sunday, are fourth on seven points.
Sergio Gonzalez hit the only goal of the night as Levante picked up their first win of the Primera Division season at the expense of Almeria. The result extends Almeria's winless run at the start of the season to four matches, while Levante move off the foot of the standings thanks to their first points of the campaign, although both sides remain in the bottom three.
In the night's other match, Real Zaragoza and promoted Hercules played out a 0-0 draw.
Zaragoza came into the match in 19th place after picking up only one point from their opening three games but they can consider themselves unfortunate not to have claimed a three-point haul after twice hitting the woodwork and now go bottom.