Gabriel Jesus scored a hat-trick on the night.
Arteta said afterwards: "Really happy. We’re in the semi-final. The game started in a way we didn’t want with a very simple goal and then the team had to react in a great way. (They) showed a lot of character and so much desire to turn things around.
"Even in the first half (when) we lacked some threat, we created two or three big chances and didn’t score. With a few adjustments in the second half we got a grip of the game again and we looked threatening."
On Gabriel Jesus, he added: "I’m so pleased for him. It’s been a long period for him without goals and today, to score three goals, the three types of goals that he scored - and the many actions he was involved in - he looked very sharp.
"I think it’s a great thing for him and the team that we can rely on a player of such quality. It’s the same with Kieran and other players who haven’t started many games and today they had the chance to do so."