Cole Palmer canceled out Kevin Schade's opener for Brentford before Chelsea took the lead through Moises Caicedo. However, Brentford earned the point with an injury-time equaliser from Fabio Carvalho.
Afterwards, Maresca said: "For sure, we were much, much better in the second half. For different reasons, we struggled in the first half. In the second half, we scored twice, so we could have scored more. But unfortunately, we lost two points in the last two or three minutes.
"I think in the second half, we scored twice. We could have scored two or three more goals. Cole had a chance, Pedro (Neto) had a chance. So I think we did enough. Unfortunately, we lost two points just in the last two or three minutes."
On learning from the result, Maresca said: "In the moment that we score the second one, we have to manage better. We scored, I think, 8/86 minutes, and in that moment, you need to give passes. You need to slow down. You need to slow a little bit the game. Something that we didn't do. And it's something that we need to improve on. We need to learn."
Asked if his players were performing with an eye on their opening Champions League tie with Bayern Munich, Maresca also said: "No, no, no, no, absolutely (not). Joao Pedro, before the game, asked me that he was not fit 100%, better (that he) doesn't play. And so if I was thinking about Bayern Munich, Joao was on the bench. But Joao played because the focus was about tonight. But for sure, when you have so many games, you have to plan a different option.
"For instance, Reece James played two games with the international team. So play tonight and thinking on Wednesday. So it's not, our focus was about tonight. And the reason why is because if this season we play Champions League, it's because we did well in the Premier League. And if we want to play again Champions League next season, we need to do well in the Premier League."