The reserves fell behind early to a Branko Strupar header, but levelled after 27 minutes through an own goal where John Sutton forced the error following a low David Galbraith cross.
After the shaky start, it was Spurs that dictated the pace and pattern of the game with some superb passing and movement against a physically strong Derby. However, in stoppage time at the end, Gary Twigg was allowed to drift into the Spurs area and he dispatched a rising shot past Lars Hirschfeld.
"I wasn't too impressed with the first 15 minutes, but once they passed the ball a little bit more simply, a little bit earlier and gave a little bit more information to their colleagues they suddenly found themselves in the game," reflected Colin afterwards.
"Although it was an own-goal we scored, it basically came the same way as the two we scored against Southampton with us breaking against teams.
"Obviously we were affected by Ronnie Henry going off and the two early substitutions.
"We had to change slightly and after that we worked our way back into the game. Once we passed the ball early and simply we began to have a little bit of joy.
"All in all - alright.
"Very disappointing to concede the last minute goal but, overall, you can tell by the crowd's reaction - they thought we played in the right manner. That's quite nice and I know myself but they've done alright to a certain degree.
"Results don't matter, I keep saying that. But when they scored in the last minute it's a bit cruel."
Colin agreed that, before Derby's winner, the team probably would have felt hard done by with a draw.
"That's what I said to them, I said 'you'd have been disappointed if it had been 1-1 and there are lessons to be learned always. When you play well, why did you play well, how did you play well?'
"When you play badly it can be a little bit more 'rough' from the end of my tounge. This time though, the manner, application and the way they went about it was first class.
"Hopefully we're going in the right direction, but they've set themselves a standard and have to keep to it."
Colin Calderwood shared the disappointment of his young side in conceding a late winner to Derby on Wednesday, but was greatly encouraged by the level of performance.