Cardiff City boss Erol Bulut told BBC Sport Wales:
"The first half was good, but the second half was not. We spoke in the dressing room at half-time. We had 45 minutes to change the game, but in the second half we didn't do anything to change the game. That is not enough.
"In the second half, this is a mentality question.
"It's not just about being safe, it's about how much you want something. Today, the opponent in the second half wanted to win, and they got it. We didn't want it in the second half, and that's why we lost three points.
"I can accept losing games but not if we aren't putting the effort in. We need to fight until the end. I demand maximum effort."
Millwall boss Neil Harris:
"Tuesday night against Leicester City was mega, it was a mega performance, today was slightly different.
"In some ways today was more important. It was a powerful message from the players.
"Every man and his dog wanted to tell me that this lot didn't know how to play at The Den.
"It was a big thing for me, I keep saying, galvanising the football club, bring the terrace and the pitch together, and yes I've played my part… but it's down to the players when they go on the pitch so they take the credit, they take the praise."