A volleyed goal by Markel Susaeta midway through the second half was enough to give Marcelo Bielsa's side the three points, but the Navarrans were superior for large periods of the match.
With the exception of the absence of the suspended Iker Muniain, the main change in Bielsa's starting line up from the side that lost to Real Sociedad last weekend was the return of veteran goalkeeper Gorka Iraizoz, who was preferred to Raul Fernandez after spending the last two matches on the substitutes bench.
The Argentinian coach's decision paid off, as Iraizoz pulled off a number of outstanding saves to keep a clean sheet and played a huge role in Athletic leaving Pamplona with all the points.
He was called into action early on, pushing a shot from Kike Sola wide after five minutes and then saving a Miguel Flano header from the resulting corner.
Iraizoz also denied Emiliano Armenteros and Alejandro Arribas in the first half, while Miguel De Las Cuevas sent two efforts over the bar.
Osasuna were the far more ambitious team, especially in the first half when Athletic created just one proper goal-scoring chance, Aritz Aduriz placing a free header over the bar.
There were fewer chances after the break, but Osasuna still looked the most likely to score.
Kike Sola showed great skill and determination down the left-hand side to present De Las Cuevas with a glorious chance, but he headed straight at Iraizoz.
Not long after, Athletic struck. Ibai Gomez cut inside from the left wing to deliver a cross with the outside of his boot which Susaeta volleyed into the net with precision.
Osasuna did all they could in search of an equaliser. Iraizoz reacted quickly to keep out free-kicks from Armenteros and Massoud respectively, and then Joseba Llorente narrowly failed to connect with a cross from Marc Bertran, but their hunt for a goal proved elusive.