Chelsea won 4-1 at Stamford Bridge on Sunday, with Joao Pedro and Liam Delap (2) on the scoresheet.
Afterwards, Maresca said: "I think the performance was very, very, very good until the red card (to Andrei Coubis). We started the way we wanted to start, intense and with a high tempo on and off the ball.
"The red card changed a little bit the game but it’s also normal (that the energy dropped a little) as Milan started pre-season on 4 July, 40 days ago, and this was their sixth friendly game.
"For us, it’s our second one. But overall, I’m very happy and now we start the Premier League."
On Pedro and Delap, he continued: "They are both our strikers, we need them scoring goals during the season, and we are very happy with both of them.
"Liam played some games in the USA (at the Club World Cup) and he scored here today. They have to be without pressure or stress, and they will score goals for sure and miss goals for sure. But at the end, they are going to help us.
"I’m confident in general and for sure excited. We have another long season ahead and we are going to try to do our best."