Steve McClaren has admitted he thought a play-off spot was beyond Derby this season when he took over as head coach.
The Rams will finish in third place in the Sky Bet Championship following Saturday's 4-2 home victory over Watford and will face either Reading, Wigan, Brighton or Blackburn in a two-legged play-off semi-final next month ahead of a potential trip to Wembley where they would compete for a place in the Barclays Premier League.
Derby were 14th in the table when McClaren succeeded Nigel Clough at the start of October. They climbed into the top-six at the beginning of December and have been there ever since.
The turnaround has surprised even McClaren, who has hailed the club's third-placed finish a "great achievement".
"Look at the squads of the likes of Wigan, Reading and Queen's Park Rangers, clubs with bigger budgets than us," said the former England manager after Saturday's game. "To finish third is a great achievement.
"I did not think it was possible looking at the teams and the squads above us, and where we were when we came in but we have achieved it.
"Credit to the players, and I am also delighted for the fans.
"What they are seeing at the moment is good quality football. They are appreciating it and the players are enjoying it.
"But finishing third is only one step. We have got bigger things ahead now, the play-offs.
"We have to keep our feet on the ground, keep our humility. We have done absolutely nothing yet.
"I said the pressure comes with 10 games to go, and the players handled that very well.
"Now the next level of pressure comes."
Victory over Watford saw Derby equal their highest points tally in a league campaign of 84 - a figure last achieved during the 2006/07 campaign when they last won promotion.
A point or more from the final league fixture against Leeds United at Elland Road at the weekend would see the Rams set a new club record.