Gary Rowett, the Derby boss, admits his side couldn't match Sheffield United's work rate as they slipped to a 3-1 defeat at Bramall Lane this afternoon.
A brace from Billy Sharp and a comical own goal from Johnny Russell saw United seal an impressive victory, despite Craig Bryson pulling one back for the visitors.
And Rowett admitted: "I think probably the first 20 minutes summed up our problems.
"I spoke to the players about what to expect. We knew it was going to be a high intensity game. Sheffield United are going to see teams like Derby coming to Bramall Lane and they will try to out-work and out fight them.
"They will out play you also but the first part of it is what they do to make it uncomfortable for teams. You have to match that intensity in any Championship game, particularly away from home and we didn't do that.
"You cannot legislate for the mistakes we made, in all fairness."