Brewers boss Jimmy Floyd Hasselbaink was disappointed to end pre-season on a flat note after the 3-1 defeat to Derby.
He said: "It was a lesson for us. I think as a unit it was the worst match we have played in pre-season.
"We have to look at the positive side of it and learn from the mistakes. You don't win anything in pre-season."
Hasselbaink was frustrated that his side did not show the usual energy even though he admitted that the Rams played well.
"It was not us," he said. "Normally we have energy. We come close to people. We press. We didn't. So it was disappointing.
Derby are a good side. They are a good footballing side, let's not forget they have players with Premier League experience, so it was always going to be difficult. Still I expected a lot more. Overall I didn't get out of it what I needed to get out of it."
One of the positives was a Brewers goal for Timmy Thiele.
Hasselbaink said: "He looked good, strong and I'm happy for him that he got a goal and could have had another one."