The Catalan giants made just two changes from the El Clasico defeat against Real Madrid, with Gerard Pique and Antoine Griezmann restored ahead of Ronaldo Araujo and Ousmane Dembele.
Barcelona launched the first threat just after five minutes as a cutback from a tight angle by Lionel Messi brought Frenkie De Jong in, but he dragged the supply against the post.
More promising openings came either end minutes later through Messi's snap effort from a difficult angle, whilst Inigo Martinez scuffed Athletic's first decent chance following a free-kick.
There was more nervy moments in store particularly for Athletic towards the half-hour mark after Messi worked an angle to curl to the near post, but goalkeeper Unai Simon gathered.
Athletic revived their initial stall just after the break in Inigo Lekue, who came on for Martinez with the Catalans unchanged from the first stanza.
However, Griezmann gave the Catalans a deserved lead right on 60 minutes after he met a clever pass from De Jong to execute from the middle of the area.
It was two 2-0 three minutes later as De Jong reversed roles to get on the end of a delivery from Jordi Alba to head in from a few yards out.
Messi joined the act five minutes later after he came short to cut onto his left and nestle the bottom-corner from inside the area.
Athletic's woes weren't over as inside two minutes Messi grabbed a brace with a sweet finish from the edge of the area following a cutback from Alba.
The Blaugrana successfully controlled the closing minutes to clinch the crown and avenge the Supercopa de Espana defeat suffered against Bilbao in January.