Nkunku struck on 86 minutes for the 1-0 win after jumping from the bench.
Maresca said: "At the end of the game I said to the players Christoph, Cole Palmer, Jadon, Joao, Noni, Mischa, Pedro, they are not going to play all the games. What they have to do is exactly what they did tonight. If I play, I have to give all my best. If I go inside for ten minutes, I have to give all my best. This will be until the end because they are seven or eight good players and we cannot play with all of them.
"Sometimes they have to be out but the important thing is they are ready when they get minutes. Christoph is doing perfect. He didn't deserve to stay out, Mischa didn't deserve but sometimes you have to take decisions.
"The good thing when they go inside is that they are ready and they give everything.
"We are still a work in progress for sure. We are learning process and again tonight if we don't understand in this kind of games we need more than the tactical part, we need the desire. It will be difficult because we want to build something important. Slowly, slowly we are going to understand these kind of things."