Jaime Mata's 56th-minute penalty was enough for Getafe to secure a first league win over Barcelona since November 2011.
Ronald Koeman suffered the first defeat of his reign as Barcelona failed to capitalise on a shock loss for Real Madrid, slipping to a 1-0 defeat at Getafe.
With El Clasico looming on the horizon, reigning champions Madrid were stunned by newly promoted Cadiz as LaLiga resumed on Saturday following the international break.
However, Barca missed the chance to move level on points with their rivals ahead of next Saturday's showdown at Camp Nou.
Jaime Mata's 56th-minute penalty was enough for Getafe to secure a first league win over their illustrious opponents since a similar 1-0 result back in November 2011, a run of 16 games.
Lionel Messi struck a post and Getafe captain Djene Dakonam was spared from scoring an own goal by the crossbar, but - after starting his reign with back-to-back wins - Koeman has now seen his side pick up a solitary point from their next two outings, laying bare the size of the task on his hands.
Ousmane Dembele made his first start of 2020 and there was also an opportunity handed to teenager Pedri from the outset, suggesting the new boss will show faith in youth during the rebuilding job required.
Still, it is a big-money signing who will once again come under the spotlight, Antoine Griezmann squandering his team's best chance to leave him still without a goal at club level in the early stages of the 2020-21 season.
The French forward wastefully blasted over when clean through in a first half consistently punctuated by the sound of referee Cesar Soto Grado's whistle, with five players shown yellow cards.
Getafe had rarely threatened before Frenkie de Jong helped them out, the midfielder clumsily catching Dakonam inside the area as he rushed in attempting to win the ball.
Mata duly converted from the spot – sending Neto the wrong way – and the dogged hosts held firm to their slender advantage through to the final whistle.
In an eventful finish to proceedings not in keeping with the rest of the contest, Juan Hernandez blazed over at one end before Getafe were saved by the woodwork in stoppage time, Barca unable to find a late leveller their performance scarcely merited.
What does it mean? Barca rebuild will take time
The underlying issues within the squad following a tumultuous 2019-20 campaign were not going to be solved by moving on some of the old guard during the transfer window. There are some early positives, but this was the first real bump in the road for Koeman.
Having failed to engineer his own exit, Messi is still around. However, so too is the dependency on him to create in attack. The visitors had 73 per cent possession but mustered just one on-target attempt.
Getafe showing fighting spirit
Rather than Barca, it is Getafe who are now on level terms with Madrid at the summit on 10 points. This was a performance that typified Jose Bordalas' side; they conceded 20 fouls and were happy to be without the ball for long spells, yet they still had more total shots and more attempts on target than the opposition.
Griezmann miss crucial
After impressing while away with France, Griezmann suffered another outing to forget when back on Spanish soil. Playing in his preferred position through the middle, his one attempt saw him badly fluff his lines. It was the kind of opening he would normally be expected to tuck away.
What's next?
Barcelona start their Champions League campaign at home to Ferencvaros in midweek, followed by a Clasico clash that has taken on even greater significance for both sides. As for Getafe, they host Granada in LaLiga action next Sunday.