It marked Delap's playing return after an early season injury, but the striker was sent off for two yellow cards.
Maresca reflected afterwards: "Very happy first-half, very upset second-half. This is the analysis and my personal view of the game. I think first-half we were very, very good. It's always complicated to go away and score three goals. We were playing nice forward, great chances.
"We didn't concede nothing and second half we were not doing the right things. Probably the first goal we conceded opened a little bit the game, gave them the boost, the energy to come back in the game. And then the three goals we conceded, I think all of them we can avoid and for sure today also we had a very stupid red card that is completely unnecessary.
"Absolutely, yes. Stupid foul, we can avoid that."
Asked what he said to Delap afterwards, Maresca said: "No, no, it's not to him, it's to everyone. I completely understand when there are red cards like Brighton or Man United that is difficult, but red card against Nottingham Forest and red card today, both we can avoid that. And we have to avoid that.
"Yes, it's embarrassing when it's a red card like today. Because it's two yellow cards in five minutes, 10 minutes, I don't know, seven minutes. Both I think we can avoid that. So it's not good."
On shouting at Delap after his first yellow card, Maresca said: "Yes, after the yellow card I told him four or five times to keep calm. But Liam is a player that when he's inside the pitch probably he'll be playing the game for himself and he struggles to realise and to listen around him."