Ainsley Maitland-Niles had a night to forget as his own goal and a Luis Suarez volley helped Barcelona to a 2-1 victory over Arsenal in the Joan Gamper Trophy.
Pierre-Emerick Aubameyang looked to have teed himself and the Gunners up for the new Premier League season in style with a fine first-half goal but Barcelona pressed in search of an error that eventually arrived when Maitland-Niles put through his own net.
It was a cruel moment for the 21-year-old in front of a huge Camp Nou crowd and Arsenal boss Unai Emery could have done without having his defender's confidence dented with a Premier League season opener against Newcastle United just six days away.
There were positives for Emery to take from the game, not least the return to action of Mesut Ozil and Sead Kolasinac after they were caught up in an apparent carjacking attempt, but Barcelona boss Ernesto Valverde will have been the happier coach at the final whistle after seeing Suarez fire a late winner.
The Blaugrauna dominated for long spells, with the midfield trio of Frenkie de Jong, Ivan Rakitic and Riqui Puig implementing Valverde's possession-based style impeccably in the absence of Lionel Messi, and the Spanish champions' patience paid off.
Maitland-Niles started positively, making inroads in possession on the Arsenal right, but he was static as Jordi Alba drifted past him before hitting a rising drive that Leno saved at head height.
Arsenal went ahead 10 minutes before the break when Ozil's incisive pass found Aubameyang with his back to goal but the striker turned Alba with an elegant piece of skill before stroking a fine finish that beat Neto to his left.
Rakitic sold Joe Willock a marvellous dummy and played Antoine Griezmann in for a sublime dink over Leno, but the offside flag was raised and the first half ended with Arsenal ahead.
Ousmane Dembele blasted wide from the edge of the box early in the second half and Willock cleared a Jordi Alba effort off the line before Maitland-Niles' nightmare moment arrived.
The 21-year-old received a loose ball in his own box and tried to play a simple back-pass to Leno but over-hit it to the goalkeeper's left, and neither Leno nor Sokratis Papastathopoulos could backpedal quick enough to keep it from trickling into the net.
Gabriel Martinelli volleyed wide as Arsenal tried to muster a response but Suarez, on as a second-half substitute, timed his run perfectly and met Sergi Roberto's floated pass with a flying volley beyond Leno shortly before the final whistle.
