Derby ran out 4-0 winners at the KCOM Stadium with two goals in each half, and the Tigers were never really at the races on a long, tough evening.
“It was a tough night,” said Crosby.
“We’ve used this competition to give some of our younger players minutes and some of the players who haven’t been playing in the league minutes. We performed fantastically well in the previous round to beat an experienced Sheffield United side, but maybe on this occasion we looked at the names on the back of the Derby shirts and perhaps gave them too much respect. Sometimes that is human nature.
“We gave Derby too much space to play. We weren’t on the front foot. We weren’t aggressive in our closing down and we weren’t aggressive with our passing when we got the ball back. That’s not taking anything away from Derby, they were by far and away the better side.
“It was a long night for us but a real learning experience for some of the younger players who were playing at the KCOM for the first time in the first team.
“We have to move on from this quickly. We play against the same team again on Saturday and we will have to be a hell of a lot better than we were tonight.”