The home side looked the most likely in the first period, but neither team could make the breakthrough with the scores level at the interval.
There was just the single goal in the second period, which proved to be the winner as Markel Susaeta found the back of the net after 63 minutes.
Read how it all unfolded in Sports Mole's minute-by-minute live commentary of the action below.
OSASUNA: Fernandez; Bertran, Arribas, Flano, Damia; Lolo, Silva, Oier, De las Cuevas; Armenteros, Sola
BILBAO: Iraizoz; Iraola, San Jose, Laporte, Aurtenetxe; Iturraspe, Herrera, De Marcos; Susaeta, Aduriz, Ibai Gomez