Mohamed Salah and Fabio Carvalho had the Reds 2-0 ahead before Kai Havertz struck a consolation for the Gunners.
Slot later said: "I think even though it's a friendly, you always want to aim for a win. You should aim for a win even if you have a small-sided game during a training session. You need to win your games, you try to do everything to win. So that's a good thing that we did that today but I'm more pleased about the way we did so. Of course I saw the second half that we had a hard time with Arsenal – they dominated possession completely.
"But we defended really well and I was really pleased to see this because a lot of bodies behind the ball every time they arrived into our 16. Real big, open chances I don't think they created in the second half. First half, after the first 10 minutes, it was an equal game, where both teams could have scored a few goals more. So, pleased to see how we played the first half and how we defended the second half."
On their young players, Slot continued: "Yeah, it's impressive. If you see that, like you said, we miss quite a lot of players that have played a lot of minutes for us last season, if you then come up to such a strong team like Arsenal had today, you're always curious to see what they can do. During half-time we had to add a few more youngsters. In the end of the game I think both teams had a lot of youngsters on the pitch.
"But it was good to see that all of them worked really hard and I think that's the first thing you have to do if you want to compete against a team that dominates possession like Arsenal did in the second half. So they did really well and I don't think one of the youngsters stood out today. The one that stood out last week, you could see today that his defensive duties, he can work on that a bit."
On goalscorer Salah's leadership, the manager added: Yes, but I don't think he's only this for this season: he has been that for several years. He came back really fit, but from what's been told to me that's normal for him. He always comes back really fit. But if I only use Mo as an example, I would not be fair to the other guys because the others are strong and fit as well. One of the main positive things until now is all the boys are fit, we have no injuries at all, so we hope we can continue like this and their fitness levels go up and up more.
"We felt today how hard it is and how tough it is to play against a team that wants to press us high – and we want to press them high. So, you need to be really fit to play games like this and we are working on this. We are heading in the right direction."