The Blues entered the fixture desperately needing a win, but it was the Tractor Boys who surged into a two-goal lead, courtesy of strikes from Julio Enciso and Ben Johnson.
Nevertheless, an improved second-half performance saw the Londoners salvage a point, though the manager insists his side should have done better.
"I think we started quite well, creating chances, then when they scored the first goal, the dynamic of the game completely changed," Maresca told Chelsea website.
"I think from then until the end of the first half, we were not good enough, especially defensively, because the two goals we conceded were both from our mistakes.
"I think that both goals we conceded, we can defend better. But if you analyse both goals, the first goal is from an Enzo long ball and then we concede. The second is a goal kick, a long ball and we concede.
"We probably lost a little bit of confidence inside the pitch because we were in control and playing well. We lost this little bit of confidence because it’s a game we must win, so when we are one goal behind.
"But in that moment, my message at half time was that we need to react and we can’t continue in the same way we were in the final 25 minutes of the first half."