Chimy Avila's late strike salvaged a 2-2 draw for Osasuna after teenagers Ez Abde and Nico Gonzalez scored their first Barcelona goals in an entertaining La Liga clash on Sunday.
Barca crashed out of the Champions League with a 3-0 defeat at Bayern Munich on Wednesday, but they looked set to respond with a battling victory at Estadio El Sadar.
Nico put Xavi's side in front on Sunday, only for David Garcia to equalise a couple of minutes later.
Ez Abde appeared to have won it with a strike early in the second half, but Avila struck in the 86th minute to rescue the home side.
Barcelona are eighth in the table and effectively out of the title race following a poor start to the season under former boss Ronaldo Koeman, who left in October and was replaced by the club's legend Xavi Hernandez.
Nico opened his account for the Catalan giants in the 12th minute, when he controlled a sublime pass from fellow teenager Gavi in an instant after timing his run to perfection and finished clinically with his right foot.
Barcelona's joy was short-lived, as captain Garcia rose unmarked to meet Jon Moncayol's whipped free-kick from the right with a powerful header into the bottom-right corner from 12 yards out.
The biggest threat
Ez Abde was the Blaugrana's biggest threat on the left and he was involved in a slick move that might have ended in a second Barca goal if Luuk de Jong had been more precise with his pass.
Barca were back in front four minutes into the second half, Ez Abde firing home from close range to round off a counter-attack after Ousmane Dembele's cross skimmed off Osasuna defender Unai García's head and fell nicely for the 19-year-old.
Osasuna were furious that the goal was allowed to stand after Gavi's clearance at the start of the break struck Sergio Busquets on the arm in the Barcelona box, but the skipper could not get out of the way.
Barca came under late pressure and were punished for failing to deal with a corner, with Avila drilling in from just outside the area with the aid of a deflection off Samuel Umtiti.
That is no wins in three games for depleted Barca in all competitions, but the performance of their gifted youngsters should give Xavi great heart.