It was the home side that took the lead after 11 minutes, however, when Ruben turned past his own goalkeeper from close range.
The away side continued to push in the latter stages and made it three courtesy of a fine finish from Miguel de las Cuevas after 69 minutes.
Read how it all unfolded in Sports Mole's minute-by-minute live commentary of the action below.
VALLADOLID: Hernandez; Rukavina, Valiente, Balenziaga, Ebert; Rueda, Rubio, Oscar, Sastre; Manucho, Bueno
OSASUNA: Fernandez; Damia, Ruben, Lolo, Bertran; Arribas, Silva, De las Cuevas, Armenteros; Nino, Sola