Frank Lampard feels his side could have done more as they fell to a 2-1 defeat at Stoke City on Wednesday night.
The Rams couldn't capitalise on playing against ten men for much of the game as former Derby star Tom Ince struck the winner just after the hour mark.
MATCH REPORT HERE
And Lampard cut a frustrated figure after the game.
He said: "We're disappointed to lose but didn't do enough when it was 1-1 and when we had the extra man. We lacked creativity and the sharpness in our passing and should have at least done enough to draw.
"It was a hostile environment but nothing you don't expect from a local derby and when you've got a manager up against his old club. The ref dealt with the one major incident - I've not seen it but I'm told it was correct - but we didn't do enough to get a point we should have got and it's also disappointing that a mistake gave them their second goal.
Skipper Curtis Davies was carried off just before half-time to add to Derby's woes further, the defender having only recently returned from a lengthy spell out.
Lampard added: "It's his achilles and could be a bad one - it didn't sound good or look good. I fear for him a bit but we'll have a closer look at it and hopefully have more of an idea tomorrow."
Derby now prepare to face Swansea City at Pride Park on Saturday.