Barcelona were held by promoted Osasuna as 16-year-old Ansu Fati became the champions’ youngest La Liga goalscorer.
Roberto Torres gave Osasuna the lead early on with a sweet volley from Brandon’s cross.
Fati came on at half-time for his second Barca appearance and headed in Carles Perez’s cross six minutes later to equalise.
Perez then set up Arthur to put Barca ahead with a 16-yard shot but Torres equalised with a late penalty.
That kick was awarded after Gerard Pique handled Oier’s cross.