Paco Alcacer scored from a free kick to save Barcelona's blushes in a friendly with second-tier Gimnastic on Friday, their first game since the departure of Neymar this week.
Lionel Messi, Luis Suarez, Andres Iniesta and Gerard Pique were left out of Ernesto Valverde's side, while Thomas Vermaelen picked up an injury.
Despite winning three games in the U.S. against the likes of Juventus, Manchester United and Real Madrid, Barcelona fell behind in the 11th minute when Omar Perdomo set up Manu Barreiro to score past Jasper Cillessen from close range.
Vermaelen then limped off a minute later and was replaced by Marlon Santos.
Substitute Gerard Deulofeu came the closest to equalising for Barcelona in the second half, but they had to wait until the 79th minute before Alcacer converted from 30 yards out.
Barcelona complete their preseason schedule with the Joan Gamper Trophy against crisis-hit Brazilian club Chapecoense on Monday, before facing Real Madrid in the Spanish Supecopa on Aug. 13.