Match ends, Celta de Vigo 4, Barcelona 1.
Barcelona suffered their biggest La Liga defeat under Luis Enrique as Celta Vigo ended the champions' 100% record in the league this season.
Former Liverpool forward Iago Aspas scored twice after Nolito opened the scoring against his former club.
Neymar pulled one back for Barca with 10 minutes remaining, before ex-Manchester City and Stoke striker John Guidetti netted a fourth for the hosts.
Barcelona had lost only one of their previous 25 matches in La Liga.
Victory took Celta briefly top of the table, but Real Madrid replace them after beating Athletic Bilbao later on Wednesday.
Barca boss Luis Enrique, said: "What decided this game is how well Celta played. It was highly effective football from them. It was very good.
"We tried to create problems, but we suffered a lot in one-on-one situations. When a team has played better than you, then there is nothing much that you can say.
"I'd rather lose to a team that plays like Celta did today, without any tricks, purely winning through their football. I congratulate them and hope they can carry on playing like that."
It was the third time Barca have conceded four goals in just nine games this season having been thrashed 4-0 by Athletic Bilbao in the Spanish Super Cup and beaten Sevilla 5-4 in the Uefa Super Cup.
- 1Álvarez Conde
- 2Mallo NovegilBooked at 79mins
- 20Gómez SolaBooked at 90mins
- 19Castro Otto
- 6RadojaSubstituted forHernándezat 76'minutes
- 18WassSubstituted forPlanasat 85'minutes
- 9Iago AspasSubstituted forGuidettiat 78'minutes
- 26Díaz García
- 1ter Stegen
- 6Alves da Silva
- 20Roberto CarnicerSubstituted forEl Haddadiat 58'minutes
- 5BusquetsBooked at 23minsSubstituted forRakiticat 66'minutes
- 11NeymarBooked at 89mins
- 2Pereira dos Santos
- 17El Haddadi
- Alberto Undiano Mallenco
- Shots on Target
Second Half ends, Celta de Vigo 4, Barcelona 1.
Attempt missed. Lionel Messi (Barcelona) left footed shot from outside the box is just a bit too high from a direct free kick.
Sergi Gómez (Celta de Vigo) is shown the yellow card for a bad foul.
Munir El Haddadi (Barcelona) wins a free kick in the attacking half.
Foul by Sergi Gómez (Celta de Vigo).
Neymar (Barcelona) is shown the yellow card.
Attempt missed. Nolito (Celta de Vigo) right footed shot from outside the box is too high. Assisted by Carles Planas.
Attempt saved. Lionel Messi (Barcelona) right footed shot from the centre of the box is saved in the bottom right corner. Assisted by Neymar.
Neymar (Barcelona) wins a free kick on the left wing.
Foul by Fabián Orellana (Celta de Vigo).
Offside, Celta de Vigo. John Guidetti tries a through ball, but Nolito is caught offside.
Substitution, Celta de Vigo. Carles Planas replaces Daniel Wass.
Goal! Celta de Vigo 4, Barcelona 1. John Guidetti (Celta de Vigo) right footed shot from the centre of the box to the centre of the goal. Assisted by Hugo Mallo with a cross.
Attempt missed. Munir El Haddadi (Barcelona) left footed shot from the centre of the box is close, but misses to the right. Assisted by Lionel Messi with a through ball.
Goal! Celta de Vigo 3, Barcelona 1. Neymar (Barcelona) right footed shot from the right side of the box to the bottom left corner. Assisted by Lionel Messi with a through ball.
Ivan Rakitic (Barcelona) wins a free kick in the attacking half.
Foul by Augusto Fernández (Celta de Vigo).
Offside, Celta de Vigo. Fabián Orellana tries a through ball, but John Guidetti is caught offside.
Foul by Jeremy Mathieu (Barcelona).