Dominik Szoboszlai proved the matchwinner on the night.
Slot later said, "I think there were a few positive things and, of course, a few things we have to improve. But the positive thing is that we kept a clean sheet. I think we only conceded one big chance and that was somewhere around the last 10 minutes of the game.
"So we controlled the game really well and in between we had a few good attacks where we created a few good chances and scored a good goal. Those were the positives from this game."
On the formation used, Slot also stated: "I think during the season you will see us play with a real striker. But at this moment we have no-one available and then with Dom and Harvey (Elliott) we've got two No.10s, so we put them in the position they will play during the season as well. So that was one of the reasons why we played with a double 10 instead of with a striker.
"That is maybe out of necessity. But for the rest of the style of play with trying to build up from the back, that is our style – to control the game, to not concede constant counter-attacks. That will hopefully be our style during the season. There are also, of course, many things we can improve but that's normal after two weeks."
On competing with Real Betis' press, he said: "I think we pressed them higher than they did us. We won the ball back a lot of times high in their half. But there were moments when they pressed us high. We played through their press a few times really good, so the goal was an example of that and our biggest chance of the second half was an example of that as well.
"But I also saw moments where we lost the ball too simple or we made the wrong choices, and I think that's normal after two weeks of trying to implement more control from the back. So, we take some positives and we take some things which we can and have to improve, especially with the likes of Arsenal and Man United coming up. "