Barcelona conceded two embarrassing goals as they suffered a shock 2-1 defeat away to Cadiz in La Liga on Saturday.
The Catalans fell behind in the eighth minute when centre back Oscar Mingueza headed the ball towards his own goal and although keeper Marc-Andre ter Stegen got a hand to the ball, Cadiz forward Alvaro Gimenez helped it over the line.
Barca drew level with a fortuitous goal of their own in the 57th when Cadiz defender Pedro Alcala diverted a Jordi Alba cross into the net, flummoxing his impressive goalkeeper Jeremias Ledesma who had been keeping Barca at bay.
Cadiz restored their lead six minutes later, however, when Alvaro Negredo capitalised on a calamitous mix-up between Barca defenders Alba and Clement Lenglet following a throw-in.
Alba aimed the throw towards Lenglet but the Frenchman could not control the ball and Negredo, on the pitch for less than a minute, ran to press Ter Stegen, blocked his kick out and dribbled the ball past the diving Frenkie de Jong and into the unguarded net.
Barca's fourth defeat of the season left them seventh in the standings on 14 points after 10 games, 12 points behind leaders Atletico, and Ronald Koeman's side have failed to win their last four away matches.
The Dutch coach criticised the attitude of his players.
"It's incredible that we lost because of a goal like that, it's an error you do not expect this team to make. It shows we were not concentrating," he said.
"The attitude was not good tonight. I'm very disappointed."
Barca midfielder Sergio Busquets said individual errors had cost them a lot of points this season.
"You cannot question the team's attitude or commitment, but when you start like we did today it makes the game very difficult," he said.
Cadiz, who recorded their first home win since returning to the top flight, moved above them into fifth place on 18 points. The Andalusians also beat champions Real Madrid 1-0 away from home earlier in the campaign.
Barca captain Lionel Messi had a frustrating night despite being rested for the Champions League win at Ferencvaros in midweek and was repeatedly thwarted by fellow Argentine and Rosario native Ledesma in the Cadiz goal.
Ledesma also kept out a stinging shot from Miralem Pjanic late on and a close-range effort from Antoine Griezmann.
Cadiz should have put the game out of Barca's reach when Bobby Adekanye raced towards goal unchallenged but failed to beat Ter Stegen.
However, their defence stood tall and they pulled off another huge win in their first season back in the top flight for 14 years.