The Catalans had begun the campaign with a 9-1 thrashing of CD Tacon, the club absorbed by Real Madrid.
But they got off to a bad start in their second home game of the season when Amanda Sampedro put Atletico in front in the second minute.
Barca hit back quickly with a penalty from former Atletico player Jenni Hermoso and moved into a 4-1 lead at halftime with goals from Mariona Caldentey and Oshoala plus an own goal from Laia Aleixandri.
Oshoala struck again soon after the interval then Atletico were further embarrassed by a second own goal, by Silvia Meseguer, which completed the rout.
Barcelona are top with seven points from three games, while Atletico have six points.