The Catalans won all seven of their opening fixtures but Hansi Flick's rotated side came badly undone in Pamplona as Ante Budimir scored a brace either side of Bryan Zaragoza's strike.

Pau Victor had given Barca a lifeline to pull them back into the game before Budimir bagged his second from the penalty spot.

Abel Bretones added a sensational fourth from the edge of the box, before Lamine Yamal pulled one back with a fine effort of his own.

Victory would have matched Barcelona's best ever start to a league campaign with eight consecutive wins, but they were not able to build on their four-point lead on second-place Real Madrid.

The Spanish champions visit Atletico Madrid, third, in a derby clash on Sunday.

"It's normal there are rotations, there are a lot of games, it's not an excuse," Barcelona midfielder Pedri told Movistar.

"In the second half we deserved a bit more but we let in goals when we were at our best."

Ahead of a Champions League match against Young Boys on Tuesday, Flick shuffled his pack.

The coach handed starts to defenders Gerard Martin and Sergi Dominguez as well as Pablo Torre in midfield and Victor in attack.

The coach rested Spain Euro 2024 starlet Yamal and Brazilian winger Raphinha among other regular picks.

As a result Barcelona failed to ignite in the first half and Osasuna winger Zaragoza took centre-stage.

Last season Zaragoza struck twice while playing for Granada in a 2-2 draw against Barca, a performance which helped earn him a move to Bayern Munich.

On loan from the German giants, Zaragoza created the opener for target-man Budimir with a fine cross, which the Croatian nodded home with ease in the 18th minute after escaping the attentions of Dominguez.

Zaragoza finished the second himself 10 minutes later after being sent through on goal, with the winger bypassing goalkeeper Inaki Pena with a fine ball roll and then slotting into the empty net.

Barcelona complained there had been a foul on Victor in the build-up but the referee waved their complaints away.

The leaders created little themselves, with the best opening falling to Ferran Torres. However the Spanish winger miscontrolled on the edge of the box and was quickly swallowed up by the Osasuna defence.

Reinforcements 

Yamal, Raphinha and Ansu Fati warmed up at half-time, with Barcelona needing to turn to their stars to mount a comeback.

Before Flick had time to send them on, Victor pulled Barcelona back into the game.

Osasuna goalkeeper Sergio Herrera gave the ball away with a poor throw, intercepted by Martin, who fed Victor.

The forward took an early shot from distance which Herrera, who slipped as he made it back to his goal, should have kept out but could not.

Flick took off top scorer Robert Lewandowski, largely uninvolved, with 20 minutes remaining and moved Torres into the middle to fill the gap.

However Osasuna almost immediately stretched their lead when 19-year-old centre-back Dominguez scythed down Budimir in the area as he went to shoot.

The striker buried the penalty with a low effort hit hard enough to beat Pena although he dived the right way.

Ruben Pena wasted a glorious chance to grab a fourth as he ran in on goal but was caught in two minds whether to pass or shoot, and Eric Garcia charged back to dispossess him as he dawdled.

Bretones, on the other hand, was lethal from the edge of the box when he won the ball back and powered an effort past Barca goalkeeper Pena.

Yamal hit back brilliantly from range and teed up Torres who struck the post, but it was too little, too late.

Osasuna rose to sixth and Zaragoza said his team had been determined to beat the leaders.

"We knew Barca were an incredible team, they had won everything and we knew we had to get stuck into it, and that's how we went out there," explained the winger.

"It's a special game and really nice to play in."