The Spaniard came in for Declan Rice in the middle of the park for the Gunners away from home.
Despite the Bees taking a shock lead, Merino and his teammates soon tool control of the game and won 3-1.
Arteta stated on Merino: “Very good. It is because he deserves it, and the type of game we had to play. The amount of density they defend with when they are deep requires people with a lot of threat in the box. He is a master of that. We believe with the unit on the left we could have the dynamics we wanted. He scored a very very important goal again. He is always there, a big threat. Great to have these options.”
He added on fellow goalscorers Gabriel Jesus and Gabriel Martinelli: “Very good timing! Both of them are really important. It is a big quality of our team, to share the goals.
“Today we have done it again, scoring in three very different ways. Great. That is what we need. The people up front have to be firing, with that feeling, and they are with that feeling right now.”
On whether the attackers answered their critics, in the absence of Bukayo Saka, he finished: “Yeah, but they are so consistent in the way they train and behave.
“They want it. Goals are about moments as well, about the feeling and energy the player is in. They are in a good mood right now.