Claudio Bravo gave Luis Enrique food for thought after a terrible error in his first start for Barcelona.
The game may have only been a friendly but the Chilean goalkeeper was to blame after allowing Blerim Dzemaili's half-volley to slip through his grasp.
Dzemaili swerving shot from range should have been easily gathered by the keeper but he let it straight through his fingers with just 10 minutes left.
It had undone an earlier save from Marek Hamsik that was out of the top drawer.
Barcelona could not fight back but they were missing their star men Lionel Messi, Neymar and Luis Suarez, whose appeal with the Court of Arbitration for Sport takes place on 8 August.
With Victor Valdes no longer at the club Marc-Andre ter Stegen will likely be the club's No 1 next season.
Ter Stegen is just 22 and 31-year-old Bravo was brought in from Real Sociedad to offer experienced back up to the young German.