Barcelona suffered a shock 1-0 defeat to Rayo Vallecano on Sunday.
Alvaro Garcia's goal just seven minutes into the league clash at Camp Nou was enough to give the visitors the three points.
It is the second time in a week that Xavi's side have been beaten on home soil, as they were beaten by Cadiz on Monday. Having also been beaten by Eintracht Frankfurt in the Europa League, they have now lost three in a row at home.
What happened in the match between Barcelona and Rayo Vallecano?
The match had a controversial ending as Barcelona appealed for a penalty when Alejandro Catena brought down Gavi.
However, the referee ignored their cries and there was no intervention from VAR.
Ousmane Dembele soon got booked for dissent as he appealed and 11 minutes of added time ended up being played at the end of the half.
The final minutes proved tense for both teams, as Jordi Alba and Gavi were booked for the hosts and Mario Hernandez, Oscar Trejo and Catena were all shown yellow cards on the opposing side.
What does the result mean for Barcelona?
Barca's upset means they are still 15 points behind La Liga leaders Real Madrid.
That means Madrid need just one point to secure the league title.
Madrid will turn their attention to Champions League action this week as they take on Manchester City in the semi-finals.
Four days later, though, they could clinch the league crown when they take on Espanyol at the Santiago Bernabeu.
As for Barca, their next match is at home against Mallorca on May 1.