The Scotland international scored a vital equalizer for the Gunners against Benfica when they were 2-1 down in the Europa League round of 32 second leg.
Asked about Tierney's goal, Arteta told reporters: "Absolutely [important goal] and you mention the right word because that is the way I would describe him, which is all determination and passion for what he does.
"The way he has come back from his injury and how willing he is to try to help the team, it gives us a big lift. After I think I have to mention the subs, because all of them, when they came in, made a difference.
"With Willian especially, I think he changed the game, he gave us much more composure, moments of creativity, he produced a goal for Kieran and we need everybody on board as this competition has the possibility to make five subs, which is a big bonus."