Arsenal won 5-0, with Nelson scoring twice after coming off the bench.
Arteta said: I think not only me but all his teammates, all the staff are so happy for him because he is a kid that is really changing, he's really evolving, he's really maturing. He's showing every day how much he wants it and today he had the opportunity, and he did extremely well because it helped us win the game.
"How mature he is, how focused he is in his profession. The way he talks, the way he reflects, the way he respects decisions, the way he is challenging everybody every single day. He is a joy of a kid. We all want him to be successful and do well. What he has done today for the team is something he really merits."
Asked if Nelson can fill in for injured teammate Bukayo Saka, he added: "We don't know first of all [about Saka]. The fact we have players that can contribute to winning games is really powerful. That is what we need when we look on the bench, to have players who can change the game. Today he has done it."