City won 4-2 in Ohio, with Erling Haaland scoring a hat-trick. Oscar Bobb also struck for City. Chelsea's goals came via Raheem Sterling and Noni Madueke.
Maresca said: "A very strange game, to be honest, because we planned the game and I think the plan was good in terms of the way we wanted to attack and defend. In the first-half, apart from the first five minutes when we conceded two goals, the team was good.
"But it is a strange game because you plan the game in one way, then you concede two goals and it changes the dynamic. What can I say about the first-half? The team was good on the ball, creating some chances, finding the right players and the right spaces.
"We had a lack of quality in the last third; especially in the one-v-one on both sides. On one side with Malo we expected that and on the other side we can do a bit better. This is the analysis of the game."
He continued: "Today we tried something different than the full-back inside. Malo was going higher and Kiernan inside - something different. For sure, we do not like to lose games but my main focus for me is to see things, different things and to try to be ready for the official games at the beginning of the season.
"Sometimes when we say something it sounds like an excuse so I do not want to say this but for sure, the pitch doesn't help. With the way we like to play, the pitch needs to be quick but it was slowing it down.
"In this moment, we need to learn things. Probably more than the goals we conceded, we need to learn that when you concede one, you cannot concede one and then after two minutes another one. This is something that I just said to the players; we need to learn. When we concede one, we need to become stronger so we don't concede another one."