Celta Vigo's 3-0 lead at half-time left Luis Enrique's side looking as ragged as they had since being thrashed by Villarreal nine years ago
Barcelona have conceded three goals in the opening 45 minutes of a game for the first time since October 2007, when they were beaten 3-1 by Villarreal.
Strikes from Pione Sisto and Iago Aspas and an own-goal from defender Jeremy Mathieu - who is having a shocker - left the Catalans trailing Celta Vigo 3-0 in the Liga clash at the midway point.
Though Lionel Messi is out injured, Barca had a chance to go top due to Real Madrid's failure to defeat Eibar earlier on Sunday.