Barcelona's table topping start to La Liga was halted as a dogged Leganes came from behind to stun the reigning champions at Estadio Municipal de Butarque.
The game was an imperfect way to mark Lionel Messi's 700th Barcelona appearance - a special feat for a magnificent player.
Ernesto Valverde handed first starts of the season to both Thomas Vermaelen and academy graduate Munir, as he opted to rest Jordi Alba and Luis Suarez.
Despite the prospect of travelling to Wembley for the Champions League showdown with Spurs just a week away, and a crunch fixture with Atletic Bilbao sandwiched in-between, Valverde traveled strongly, with Messi, Coutinho and Dembele leading the line for la Blaugrana.
Leganes, meanwhile, came into the match winless, with just one point from their opening five La Liga games.
Coutinho opened proceedings with a sumptuous volley after just 11 minutes, after a wonderful pass from Lionel Messi.
Just five minutes later, Messi nearly brokered his way onto the score-sheet as his curling effort ricocheted off the bar and out for a goal-kick.
After being wholly dominated throughout the first half, Leganes came out after the interval as a completely different team.
El Zhar nodded Leganes level on the 51st, before more woeful Barca defending saw Rodriguez take advantage of a Gerard Pique blunder to smash home a second in the 52nd minute.
Barcelona came close to grabbing an illusive equaliser in the final 30 minutes, but Ivan Cuellar as on hand to pull off a stunning double save to condemn Barcelona to a disastrous defeat.
See our breakdown of the game below.
Key Talking Point
Barcelona, wearing luminescent yellow, started brightly. Coutinho's precise volley found the far corner before Messi rattled the bar just five minutes later.
Despite this, the key talking point will be the concession of two quickfire goals in the second half.
Phillippe Coutinho - The stand out performer in a very average Barcelona team. Brilliantly firing Barcelona into the lead after 11 minutes, Coutinho and co. looked set to waltz past Leganes
Despite this, Coutinho only called Ivan Cuellar into action one more time throughout the following 80 minutes as he and his Barcelona teammates failed to see off a team set for a La Liga relegation battle this season.
Munir - Despite a number of Barcelona players under performing, Munir struggled to impress on his first La Liga start of the season. Appearing to be feeling the weight of the badge, Munir had more of an impact apologising to his teammates rather than threatening the Leganes goal.
Been wondering why we called Munir the new Messi— prateek (@pbthegrea) September 26, 2018
What a scruffy first half from Barcelona we have been poor away from home, the passing is very slow and we seem to lack ideas— Ultimate10 (@ClassicMessi10) September 26, 2018
All the games we've watched for Barcelona so far this season have been boring and stressful as f*ck. Imaging still defending the donkey Valverde..— Marie-Anne (@PlQUECHU) September 26, 2018
Ernesto Valverde's men entertain Atletic Bilbao on Saturday, who find themselves without a win in eight La Liga fixtues against Barca.
Following this, a trip to England and Wembley Stadium awaits, as Tottenham Hotspur play host for group game two in pot B.