Los Rojillos showed plenty of early intent, especially with balls behind Barça’s youthful backline, although the visitors initially stood firm with Eric Garcia flying out to block a Bryan Zaragoza strike.
Ante Budimir then made a burst up the pitch on the quarter-hour mark before smashing an attempt that fizzed agonisingly wide of the far post.
The Croatian opened the scoring soon after, as Bryan worked some space from Jules Kounde and delivered an inviting cross that Budimir reached ahead of Pau Cubarsi and clinically headed home.
Osasuna were relentless and caused another scare, as Inaki Pena rushed out of his box and could only clear to Ruben Garcia, whose attempt hit Budimir.
Pena was left helpless on the floor moments later, as Bryan latched onto Pablo Ibanez’s perfectly weighted through ball and audaciously rolled it around the goalkeeper before scoring.
The Blaugrana regained some semblance of control but were unable to find Robert Lewandowski with their balls into the box, and Kounde came closest seconds before the break with a header that hit the crossbar.
Barça finally got Lewandowski more into the game after the restart, but the striker hit a free-kick agonisingly wide and he was then denied by Sergio Herrera.
The goalkeeper gifted the visitors a way back into proceedings moments later, though, throwing the ball straight to Gerard Martin before failing to stop Pau Victor’s shot as he stumbled back.
Lamine Yamal and Raphinha were introduced with Osasuna pinned back just before the hour mark, although the hosts fought back and Budimir came close before Ferran Torres ghosted through but was denied by Herrera.
Budimir then regained his side’s buffer, winning a penalty from Sergi Dominguez that he sent out of Pena’s reach.
An outstanding evening was then capped off with an equally impressive strike from Abel Bretones in the 85th minute.
Even though Yamal responded with an exquisite goal of his own, Osasuna earned a fourth consecutive victory at El Sadar in a single La Liga campaign for the first time since March 2008.
That achievement is made even more special as they defeated a Barcelona side who previously had a perfect record in the league this term.
Flashscore Man of the Match: Bryan Zaragoza (Osasuna)
