Postecoglou was informed of the decision by Forest owner Evangelos Marinakis just ten minutes after the final whistle.
After the 3-0 win at the City Ground, Maresca began: "I didn't speak with Ange. I didn't see him. I feel sorry for him.
"This is a business if you don't win games, the consequences are the same for everyone. I'm sorry for him."
Maresca watched the game from the stands as he was suspended for the day. Josh Acheampong, Pedro Neto and Reece James struck for Chelsea, with Malo Gusto sent off late on.
The Blues manager continued: "Very bad feeling to be there (in the stands), I prefer to be in the dugout. We struggled in the first-half.
"Second-half we were better. We could do better in terms of the red card, we can avoid that. The desire of the players not to concede a goal was important. They were shouting at each other not to concede in the final few minutes. It's important."
On Gusto, Maresca said: "Again, it's something we can do better. But I am not concerned. There are some of you who ask why I am not concerned.
"We can avoid it, for sure, but for me, the desire of the players is important. It's useless to make a second yellow card with a foul but Malo showed his desire. It's the balance but we can avoid that, for sure."
On Acheampong's performance, the Italian also stated: "I really like Josh. We showed him confidence last season. He is doing well. It's important that he is ready when others are out.
"He needs to improve, for sure. It's our duty as coaching staff to help players improve. We are working every day to try and improve him and the team."