Barcelona is still third in La Liga, thanks to a late own goal at Rayo Vallecano.
Barca dominated the second half despite trailing at the halftime to Unai Lopez’s sensational strike.
They were rewarded when Florian Lejeune bundled into his own net while under siege from Robert Lewandowski.
Second-placed Real Madrid will play Cadiz on Sunday before Girona hosts Athletic Bilbao on Monday.
Barcelona made six changes from the team that beat Alaves before the international break, with goalkeeper Marc-Andre ter Stegen out due to injury.
His replacement, Inaki Pena, looked shaky from the start and was defeated midway through the first half by Lopez’s thunderous right-foot attempt.
Frustrated with his team’s disorganized performance, Xavi brought in former Manchester City captain Ilkay Gundogan from the bench, and Barcelona dominated the second half.
Despite taking ten shots after the break to Rayo’s three, they still needed Lejeune’s assistance in the 82nd minute, when he awkwardly slid the ball past his own goalie with Lewandowski waiting to pounce.