Cadiz pulled off a shock 2-1 win over Barcelona in La Liga on Saturday night, piling on to the mounting troubles for the Blaugrana in their domestic campaign this season.
The hosts took a shock lead from a corner kick when Marc-Andre ter Stegen palmed the ball into the path of Alvaro Gimenez, who simply had to tap it into the net to make it 1-0.
The goal seemed to enliven Barca, who were firmly in control for the remainder of the half, but save for a near miss by Martin Braithwaite the visitors could not score and went into the half-time break trailing.
Barca continued to dominate possession and drew level just before the hour mark when Messi played in Jordi Alba and his shot from a tight angle took a fortuitous deflection to beat Cadiz keeper Jeremias Ledesma.
However, Cadiz took the lead again minutes later when a miscommunication between Clement Lenglet and Ter Stegen following a throw in left Alvaro Negredo alone for a simple tap in to Barcelona's open net.
Barca poured on the pressure down the stretch and Messi saw two good chances go right to Ledesma, but Cadiz were up to the task and saw out the match to take all three points and stay ahead of the Catalans in La Liga.
The win was Cadiz's first over Barcelona since 1991 and put them just outside the Champions League places in the table. The Andalusians also beat champions Real Madrid 1-0 away from home earlier in the campaign.
Barca's fourth defeat of the season left them seventh in the standings on 14 points after 10 games and Koeman's side have failed to win their last four away matches.