Eidur Gudjohnsen's late strike gave Barcelona a 3-2 victory at home to Real Betis after the Catalans had thrown away a two-goal lead.
Samuel Eto'o put Barcelona in front after 17 minutes and the Cameroon striker doubled the hosts' advantage shortly afterwards.
But Betis improved after the break and pulled a lucky goal back through Luciano Monzon on the hour.
And the Andalusians stunned the Nou Camp with a shock equaliser eight minutes later, when Jose Mari took advantage of some poor Barcelona defending to level the scores.
Barcelona appeared to have put their early-season troubles behind them following the stunning 6-1 thrashing of Sporting Gijon on Sunday night.
In that game, Pep Guardiola's side found the attacking verve missing from the opening day defeat at Numancia and the disappointing home draw against Racing Santander in the second round of matches.
And they picked up where they had left off against Sporting with some lovely football in the opening stages.
Betis lined up with a five man wall in midfield, but Barcelona looked capable of scoring every time they went forward.
Lionel Messi almost set up Eto'o after eight minutes, but Melli cleared the ball away for a corner.
A minute later, Andres Iniesta went down in the area following a heavy challenge from Nelson, but the referee waved away the penalty appeals.
However, Barcelona soon went ahead, when Messi cut inside and found Eto'o unmarked on the edge of the area.
With the drop of a shoulder and a quick change of pace, the African striker beat his marker and lashed an unstoppable drive in off the crossbar, giving Betis keeper Casto Espinosa no chance.
Five minutes later, Messi took up possession in a similar position, waltzed past Fernando Vega and cut the ball back for Eto'o to tap into the net from close range.
Both goals were typical Barcelona and the home side threatened to add to their tally before the break.
Messi saw a low shot well saved by Casto and Brazil full-back Dani Alves also came close to a third.
Iniesta saw another penalty shout turned town after a questionable challenge by Nelson.
But after the break, Betis improved vastly and began to trouble Barcelona.
Jose Mari fired wide after 56 minutes and Capi forced Victor Valdes into a fine save in the visitors' next attack.
Paco Chaparro's side then got the lifeline they needed on the hour mark, when Monzon deflected an indirect free-kick past the helpless Valdes.
And the visitors levelled the match after 67 minutes, when Jose Mari got in behind a dormant Barcelona back-line to lob the ball over Valdes and leave the Nou Camp stunned.
Guardiola's side looked shaken and the coach rang the changes in the latter stages.
Bojan Krkic, Sergio Busquets and Gudjohnsen all came on as Barcelona looked to salvage the two points which had slipped from their grasp within the space of eight minutes.
But the Catalan defence remained shaky and Sergio Garcia almost gave the visitors the lead after 76 minutes, when he fired just over on the turn.
After that, though, it was all Barca.
Bojan saw a stinging effort well saved by Casto after 79 minutes, but Gudjohnsen struck the winner with an angled shot a minute later to send the Nou Camp into raptures.