Nathan Jones was disappointed with his side's performance on Tuesday evening, as they fell to a 3-1 defeat at home to Portsmouth.
"The majority of the game we were dominated physically," he said.
"The first goal is a really poor one to concede, no one closed him [Terry Devlin] down and then it went straight through our goalkeeper, and that can't happen.
"The penalty is subjective. We had better chances, we had clear-cut chances, but the all round performance tonight was really poor.
"Today was not the messages we give. It's 11v11 out there and they wanted it more than us and that is unacceptable.
"If you don't do the basics well then you can't have a platform in the Championship.
"The first goal is a goalkeeping error, he has to save that. The second one we have to look at, but it was that kind of night."
Jones made three changes at half-time, bringing on Jayden Fevrier, Tyreece Campbell and Conor Coventry and adjusting the team's formation.
He said: "With the changes, we had to lay a glove on them and be stronger, and have more of a threat.
"[Jayden] Fevrier had a real impact when he came on, I don't like making that many changes, but we were poor tonight.
"I thought there was a lot going on in the game, everything first half was a booking. In my opinion, the referee got a hell of a lot wrong tonight and he contributed to that type of the game, but that didn't impact the outcome.
"It is not just the goals we conceded, it is the level of the performance I am not happy with.
"As much as there was glimpses of quality, there was a massive part of it that isn't us.
"It was a tough one to take, but we have to go again."
