Anthony Elanga and Jacob Murphy scored for Newcastle. Arsenal won through goals from Mikel Merino, an Alex Murphy own goal and a penalty converted by Martin Odegaard, which was won by 15 year-old Max Dowman.
Afterwards, Arteta reflected on Martin Zubimendi's first showing: "Very good. I think the demand that Newcastle put on you, especially in midfield, with the kind of plays and profiles that he had, I think he coped with it with intensity, with the physicality.
"He's so smart, he's one step ahead constantly, he can read situations, he can execute at higher speed, whether he has space or not, and that's not a common thing to have in a player, especially when you're a midfield player."
On Dowman winning the decisive penalty, Arteta admits he was impressed.
He said: "Yeah, it is special. Obviously what he's done today against this team in the time that he had on the pitch is something certainly not common to witness for a 15-year-old. We are extremely happy to have him.
"I think again the environment that he's around in, his family, the people at the club and around the academy as well, super helpful because they put him into this position so early in his journey, having a real chance and a real presence when he plays for the first time."