Preston won 1-0 thanks to Robbie Brady's long-range drive. Mohamed Salah and Dominik Szoboszlai were among the starters for the Reds.
Slot said afterwards: "I've seen this a lot during the training sessions, maybe a bit more than today but that also had to do with the playing style of the opponent.
"We controlled the game completely and only conceded one shot. We were a bit unlucky to lose 1-0 given we only conceded the one shot.
"We had some good build-up moments and had some good chances in the first half, the second half I didn't think we created that much which is normal because there were a lot of young players in the team who didn't play in their normal position sometimes as well.
"We couldn't have asked more from the boys in the first two weeks. We've worked really hard, tried to implement ideas and it's not that we're only bringing new ideas, a lot of things that have already been done here have been really good."