The 32-year-old moved to the Emirates Stadium from London rivals Chelsea in the summer but has struggled to make an impact.
“He is a player who we all like," Arteta said of Willian.
“His team-mates like him and we were expecting many more things from him since he joined but for many different reasons he hasn't found his best performances.
“But hopefully Thursday's performance is going to give him the platform and belief that he is a really important player – he is a player I really like and I did a lot to bring him in and hopefully he can still give us more.
“I was really pleased with Willian on Thursday and he totally deserves some credit because of the way he trains every day and he is trying.
“In games now you can see that he is starting to produce what we think he can do for the team so everyone has to step up and create big moments in games because the front players in the end have to be the ones that decide the game for us."