Clement Lenglet scored a 91st-minute header to spare Barcelona's blushes and secure a last-gasp victory away to Cultural Leonesa in the Copa Del Rey third round.
The French defender, who came on as a substitute in the second half, powered home in stoppage time after a lacklustre display from the La Liga champions.
Ernesto Valverde decided to rest the likes of Sergio Busquets and Luis Suarez for the trip and included several B team players in their starting XI, a move which nearly backfired.
The Catalan giants looked off-colour throughout and only had their first shot on target in the 71st minute, despite starting the game with a frontline worth £150 million in Ousmane Dembele and Malcom.
Ultimately though, it was summer arrival Lenglet who struck late on to take the slender advantage back to the Camp Nou for the second leg.
Meanwhile, Real Madrid thumped Spanish minnows UD Melilla 4-0 in Santiago Solari's first game in charge as interim coach.
The La Liga giants had sacked Julen Lopetegui on Monday evening after the humiliating 5-1 Clasico defeat to Barcelona and placed Solari in temporary charge as they search for a successor.
But even in a game they were expected to win comfortably, things looked promising for the Spanish side. Karim Benzema opened the scoring before Marco Asensio struck on the stroke of half time.
Goals in the second half from Alvaro Odriozola and youngster Cristo in stoppage time made sure of the victory which will provide a boost in morale ahead of Saturday's game against Real Valladolid.
