Neil Harris has reflected on Saturday afternoon's defeat to Preston North End at The Den, stating that the "damage was done" by half-time.
Millwall trailed 3-0 at the break against Alex Neil's side, and Harris notes that he perhaps did not select the correct starting XI for the contest.
"The damage was done in the first half, which wasn't acceptable. We conceded two goals from set plays which we got all wrong, and it's about defending your goal," the manager says.
"It wasn't just the goals, it was the lacklustre first half hour which I don't expect from my players at The Den. I take some responsibility in myself that maybe I picked the wrong team and should have made more changes - I saw it that against a fast, physical Preston side, you don't want to change too much after the performance on Wednesday night at Derby.
"The two performances were chalk and cheese. What I will give credit to my players for is the second half display, yes, we were very attack-minded and left ourselves open on the counter-attack, but we should have got back into the game with the number of entries we managed to get into the penalty area."
With League matches coming thick and fast, Harris is adamant that performance levels must be raised for Tuesday's visit to Hull City.
"We didn't deserve anything from the game and it's a reminder to us after the euphoria of Wednesday night that that's Championship football. We're about to face another opponent of similar quality in Hull, so we certainly have to reach our levels which we've reached various times in the last eight weeks.
"Anyone who thought it was now going to be plain sailing until the end of the season is hugely mistaken. This is the toughest Championship division I've been in for a long time and today just shows it.
"Alex [Neil]'s pre-match teamtalk would have been about getting after us and putting us under pressure, whereas ours was about starting well and showing that we've recovered well from Wednesday. They got the ball in behind us quickly and with quality, and we didn't. We were a yard off it all over the pitch."
The boss made the decision to withdraw Tom Elliott and Murray Wallace after 45 minutes, and replaced Ryan Leonard with goalscorer Ben Thompson just after the hour, with the midfielder getting on the scoresheet just moments later.
"Tom and Murray certainly weren't any worse than anyone else on the pitch for us in the first half - if I could have made more subs at half-time I would have done, I would have brought Ben on earlier if I felt that I could make three changes at the break," Harris explains.
"I was worried about legs in the second half, but when it got past the hour I thought we needed Ben on the pitch, and when he came on he was excellent.
"There were players who didn't live up to the expectation they've set in the last eight weeks, and there were some who did - particularly in the second half, and Ben was very much in that category."