We had enough chances in a 20-minute spell in the first half to have wrapped up the game before Lee Morris struck what turned out to be the winner just before the break.
The introduction of Matthew Etherington, rested Darren Anderton and Sergei Rebrov in the second half failed to change things around as John Gregory won his first game in charge of the Rams.
Boss Glenn reflected: "We had possession but didn't do enough to create chances with the possession we had.
"It was a miserable feeling coming in 1-0 down at half-time when you've had that amount of possession but possession doesn't win games."
Glenn was also concerned with what he described as a lack of 'driving force' in the televised encounter.
He said: "It was an awkward time to come and play Derby. They were lacking in confidence and if John hadn't arrived, I don't think the support from the crowd would have been the same.
"They got their energies up for the players and were prepared to get behind them whereas a couple of weeks before it might have been a different story.
"But we knew about that, we spoke about it, that they would have an extra spring in their step and we would have to match it.
We matched it in football terms in the first half but we didn't really have a driving force there.
"I just felt there was a little lack of real determination as a team to go out and win it. That's something we'll have to have against Bolton on Tuesday."
Glenn Hoddle was once again left to rue the failure to capitalise on possession at Pride Park on Saturday.