Chelsea were beaten in the second-leg 2-1, but progress to the group phase 3-2 on aggregate. Christopher Nkunku had Chelsea ahead before Servette came back to win the second-leg through Jeremy Guillemenot and Enzo Crivelli, but they couldn't find a third goal to take the tie into extra-time.
Maresca said: "I think the first half an hour we scored a goal and had three or four more chances, and if we were able to score then the game was finished because it would have been 2-0. And then we conceded a goal and it's normal to suffer a little bit.
"I told you yesterday but I was very, very worried about this game because they are tricky games. For them, it's probably the game of their season. Against us, the pitch is not great, the environment, it's 30 degrees and I was very worried about the condition of the game.
"On and off the ball, the team was very aggressive. We created four or five chances in the first-half and if we score, the game is finished. Then it is football - they score and it's a boost for them. But in the end, we deserved it, so we are happy.
"In this kind of game, in the end you have many things to lose and not many things to win. But this is the reason why I was so worried yesterday and before the game. But the way we started, the way we played in the first half an hour was unbelievable.
"On the ball, we were very good and then we conceded a goal. It then becomes a bit more difficult."
He also said: "It is a competition where we are going to try and do our best in. I think tonight, once again, the team shows in the way we started that the team was there. Then the game, we concede; they had some chances and we lost a little bit of confidence.
"But overall, even in the second-half I am now thinking a bit that I remember three times one-v-one with the goalkeeper. In the end, if we are able to take the chances, especially in the first-half when we are 1-0 up, if we are able to score the second one then the game is finished.
"It's one more competition. We have Conference League, Premier League, FA Cup, the Carabao Cup - they are all competitions where we are going to try and do our best and then we will see where we arrive."