Concise News reports that just seconds after coming on as a substitute, the veteran striker showed that there are still plenty of goals left in him with a superb scissor-kick to win it for the home side.
Without talisman Lionel Messi, the Barcelona attack did not really sparkle, and things were not helped by Luis Suarez having to exit the field in the first half due to injury.
New arrival Antoine Griezmann and compatriot Ousmane Dembele were largely anonymous in a performance to forget for the Catalans.
Ivan Rakitic and Sergio Busquets started from the bench, while Frenkie de Jong, Sergi Roberto and Carles Alena made up the midfield.
Athletic roared out of the gates and Inaki Williams came close to scoring the first goal of the La Liga season, but Barcelona goalkeeper Marc-Andre ter Stegen showed no summer rust by making a pair of stretching saves.
A horrific error from the Athletic defence almost resulted in the first goal as a back pass was played right to Suarez, but the Uruguayan hit the post.
Shortly before the giveaway, Suarez appeared to have pulled a muscle and had to be replaced by Rafinha Alcantara, with Griezmann sliding into the centre-forward position.
Barcelona then hit the woodwork a second time before the break when a curling effort from Rafinha forced Unai Simon into pushing the ball onto the crossbar and out.
Valverde made his second change during half-time break, with Alena making way for Rakitic in the hope of having more control over the midfield.
While Barcelona saw more of the ball, they remained stale in attack and did very little to trouble the Athletic back line, except for a Rakitic shot that rocketed over the crossbar.
The last change for Barcelona came with 15 minutes remaining as youngster Carles Perez got a shot to make a difference, coming on for Sergi Roberto.
A solo effort from Rafinha almost gave the match a jolt, but it deflected wide.
Just when it looked like things would end goalless, Aduriz came off the bench to replace Inaki Williams and a minute later, the 38-year-old scored what will go down as one of the best goals of the Spanish season by defying his advancing age and sending in home a scissor-kick, which saw Athletic emerge as 1-0 winners.