An injury-ravaged Barcelona conceded a late equaliser despite the best efforts of their young players as Ezequiel Avila fired in an excellent effort for Osasuna on Sunday night.
The visitors took the lead in the 12th minute when two of their youngest stars combined, Gavi lobbing a ball into the box for Nico to control nicely and curl beyond Sergio Herrera.
Barça's perfect start was wiped out shortly afterwards as David Garcia rose highest to glance in Jon Moncayola's free kick, with some non-existent defending helping Osasuna draw level.
Xavi's side took the lead in the second half, though it wasn't without a tinge of controversy.
The hosts were convinced they should have had a penalty when a clearance smacked Sergio Busquets on the arm, but nothing was given and the ensuing counter attack saw Abdessamad Ezzalzouli smash a half volley into the top corner.
Barça looked vulnerable from set pieces all night and their failure to properly clear one late on Avila latch onto the ball on the edge of the area. The Argentine rattled one past Marc-Andre ter Stegen, condemning the Blaugrana and Xavi to another disappointing result.
The result means Barcelona remain eighth in La Liga, while Osasuna have jumped up one place to tenth.
BARCELONA PLAYER RATINGS
1. Goalkeeper & defenders
Marc-Andre ter Stegen (GK) - 5/10 - Couldn't get near Garcia's excellent header but looked heavy on his feet throughout the game. Sliced a clearance at one stage but got away with it. Got booked.
Ronald Araujo (CB) - 6/10 - Did well to shut down some promising Osasuna attacks.
Gerard Pique (CB) - 7/10 - Made a game-high six interceptions. Could have done with a more composed Umtiti alongside him but he did all he could. Booked and will miss his side's next game.
Samuel Umtiti (CB) - 4/10 - A few shaky moments, giving away a needless corner in the opening 20 minutes with a loose pass. It was his first appearance of the season so some rust was to be expected, but it was still a dodgy performance.
2. Midfielders & wing backs
Ousmane Dembele (RWB) - 7/10 - His free kick from out wide almost set up Abde and then Umtiti, but offside was given regardless. Played the ball across goal that led to Ezzalzouli's strike. Pretty good defensively too, making three tackles.
Nico (CM) - 7/10 - Great control and composure to take Gavi's cross and finish for the opener. Always looked to get on the ball, taking responsibility while his side were in possession.
Sergio Busquets (CM) - 7/10 - A cool, calm head when those around him showed a bit of inexperience. Had a scare when a clearance struck him on the arm before Ezzalzouli's strike. Some good interceptions and trademark swivels on the ball.
Gavi (CM) - 7/10 - Wonderful cross picked out Nico early on. Earned a yellow card for a cynical challenge. Barça's most proficient passer, completing 91% of them.
Abdessamad Ezzalzouli (LWB) - 8/10 - Some nice jinking runs down the left. A really nice finish - slamming the ball into the back of the net - gave Barça the lead in the second half. Was a constant threat and may have ended up with a few more goal involvements on another day.
Frenkie de Jong (AM) - 5/10 - Started further forward but retreated into a deeper role late on. Couldn't put his stamp on the match, Lacking that spark that made him so special at Ajax.
Luuk de Jong (ST) - 4/10 - Butchered a good counter attacking opportunity with a poor touch and pass. Injuries forced Xavi's hand for this fixture but it's safe to De Jong does not look like he'll be a Barcelona player for that much longer.
Oscar Mingueza (LB) - 6/10 - Made a couple of tackles after coming on in the 72nd minute.
Philippe Coutinho (RW) - 5/10 - Only had eight touches following his late introduction.
Ferran Jutgla (LW) N/A - A proud moment for the 22-year-old as he came on in injury time for his Barça debut.