After an 8-1 aggregate victory over Minsk last October, the Nigeria international played a key role to help the Catalans seal their progress to the last four of the tournament.
Oshoala, who had scored 26 goals in 26 appearances this season, was handed her fourth Champions League outing this term and made her sixth meeting with Atletico since arriving in Spain.
Lluis Cortes' team enjoyed the bulk of possession but could not find a breakthrough past the rock-solid defence of Atletico as both teams went into the half-time break tied.
After the restart, Barcelona continued with their dominance but failed to break the resistance of Dani Gonzalez's side until Oshoala's miscued acrobatic effort fell into defensive midfielder Kheira Hamraoui's path, and she duly grabbed the winner 10 minutes from time.
VIDEO: Nigeria captain @AsisatOshoala made her presence count with an assist as Barcelona squeezed past Atletico Madrid to the semi-final after a 1-0 quarterfinal win in Bilbao.#AtleticoBarca #ATLBAR #UWCL pic.twitter.com/3786rAJkNW— Samuel Ahmadu (@sam4wigan) August 21, 2020
Oshoala, who was in action for 82 minutes before being replaced by Aitana Bonmati, has now contributed an assist and a goal in five outings for Barcelona in the competition this season.
The 26-year-old striker has now been involved in Barcelona's last five victories against Atletico in all competitions, scoring four goals.
She will hope to help Barcelona continue in the same vein in the semi-final of the tournament on August 25 when they take on Wolfsburg, who humiliated Glasgow City 9-1.