Having come off the back of a 6-3 defeat at the hands of Chelsea, Mirallas believes that Everton responded "very well" versus the Baggies.
"The most important thing was to win the game. The team played very well," the Belgian international told the club's official website.
"After the game against Chelsea it was difficult but the team has been training hard and prepared really well. At West Brom, we scored two goals and kept a clean sheet. It was a great day."
Everton start their Europa League campaign on Thursday night when they welcome German side Wolfsburg to Goodison Park.