The Barça captain Alexia Putellas opened the scoring when she headed in from close range after Caroline Graham Hansen’s shot deflected into her path. She doubled Barcelona’s lead after a header from Esmee Brugts had been saved.
Bonmatí got in on the act shortly before half-time and doubled her tally with a firm finish into the far corner.
“It’s good to start the season in the Champions League, scoring five goals in front of our own fans. We want to keep going for more,” said Bonmatí.
Elsewhere, Ada Hegerberg scored her 60th Women’s Champions League goal as Lyon opened their campaign with a 9-0 demolition of Slavia Prague. Kadidiatou Diani and Vanessa Gilles scored twice in the Czech capital.