Following her back-to-back scoring exploits, Lluis Cortes handed the Nigeria international her fifth start of the season and she made the best of her chance to inspire her side s eighth successive win.
Desperate to reclaim the top spot, Aitana Bonmati set up Mariona Caldentey to open the scoring for the visitors after just one minute.
In the 28th minute, Caroline Graham Hansen provided an assist for Caldentey to double Barcelona s lead with her second of the tie before the Norwegian got on the scoresheet seven minutes later.
Six minutes from the break, Hansen assisted Oshoala to net a fourth before the Nigerian was teed up by Patri Guijarro to bag her brace and the fifth for the visitors on the brink of half time.