Viktor Gyökeres scored twice — taking his season tally to 21 — and Bukayo Saka also netted as Arsenal completed all three first-half goals before the break. Gyökeres, who also assisted Saka's finish, becomes only the second Arsenal player in the past 25 years to reach 20 goals in a debut season, following Alexis Sánchez in 2014/15.
Arteta made five changes from the side that drew 1-1 with Atlético in Madrid on Wednesday, and the freshness was visible from the opening minutes.
"I'm really, really happy," he said. "I think it was a big performance, a very strong team performance, and a very impressive individual performance as well from the boys. We came back from Madrid on Thursday afternoon, also playing a game that took a lot from us, energy-wise, mentally, but the team responded incredibly well."
He identified the moment the week's momentum began to shift.
"I got a really good feeling on Thursday when we had a meeting before we got on the plane, because we talked about everything that we have to do now. It's about energy and showing how much we want it, and that hunger. And the team clicked immediately, the boys delivered what we planned against a really tough opponent, and we were very efficient."
On the attacking combination of Saka and Gyökeres, who created and scored from two of the three goals having barely played together this season due to injuries, Arteta was equally satisfied.
"They haven't played together much unfortunately because of the injuries we had, but there were a lot of relationships that I really enjoyed today."
He singled out Gyökeres for particular praise.
"We need players in a big and positive emotional state now, and he's certainly one of those. He feels confident, he's scoring very important goals as well, and that's going to be key for Tuesday."
Myles Lewis-Skelly's debut start in midfield also drew a pointed admission from the manager. Asked why he had waited so long to deploy the 19-year-old in his natural position, Arteta was candid.
"Because probably I don't have a clue and maybe I should have done it earlier, I don't know. But I have to do things when I believe that the player is ready, the team is ready and the opponent is the right one. We've done it today, it's the first time. He fully deserves it."
On Tuesday's second leg, Arteta left no ambiguity about the mood inside the dressing room.
"I can't wait. I saw the energy now in the dressing room and we are all ready for it. Let's create something unique and let's get to the final."