Bryan Mbeumo had Brentford ahead before Gabriel Jesus, Mikel Merino and Gabriel Jesus struck for the visitors.
Arteta said afterwards: "We won in a difficult stadium, against a good opponent. The record they have here is incredible and when you go 1-0 down it makes it even harder.
"We have to navigate through some difficult moments.
"We started really fast and aggressive and again adapting. We had some injuries and sickness and we had to play some different players."
On Gabriel Jesus' form and different goalscorers, he said: "Very important. Today Martinelli scored and Mikel scored from a set-piece.
"In the last calendar year you see who has scored for us and that's our strength.
On Ethan Nwaneri's performance, Arteta added: "Really good. In training he gave us all the right reasons. He is an academy player and he needs to play because he deserves it."