Middlesbrough head coach Aitor Karanka was left deflated after Boro were defeated a heart-breaking late goal.
Ten-man Boro were scuppered as super-sub Connor Sammon scored a late winner for Derby and former Middlesbrough boss Steve McClaren.
McClaren won the League Cup and reached a UEFA Cup final during his tenure as Middlesbrough boss and, in his first managerial game against his old club, he saw his new team emerge somewhat lucky winners as the Teessiders’ brave resistance was finally broken.
Chris Martin had given Derby a 33rd-minute lead with his 10th goal of the season after Boro’s Curtis Main was dismissed.
Dean Whitehead restored parity, before Sammon’s late strike clinched a 2-1 win and the spoils for the Rams.
Despite Sammon’s late intervention, Karanka was pleased with his side’s application on the night.
“You can’t be sad when you lose one game,” said the ex-Real Madrid assistant boss.
“To concede goals at the end of both halves, we felt bad. I saw I have a team which is together, everyone was helping each other and fighting the same battle and I was very happy about that.
“It was very encouraging. When you lose the way we did, you cannot really say anything to the players.”
Karanka was left baffled by Main’s red card, which came after his lunge on Derby defender Jake Buxton and saw him booked for the second time inside 10 first-half minutes.
“I would like to know why he was sent off,” went on Karanka. “If he deserved two yellow cards, then you would be ending every game with six or seven players.”
He dropped Mustapha Carayol to the bench, but brought him at half-time and was rewarded when the winger’s trickery set up Boro’s equaliser and he was delighted with his display.
“The fastest player I had on the bench was Muzzy and I was thinking of keeping (Kei) Kamara and (Albert) Adomah on the wings, and so play him up front with his pace,” added the 40-year-old Spaniard.
“He played very well and I was very happy with his work.”
Dean Whitehead and Main came in for suspended Boro skipper Grant Leadbitter and Carayol.
A cagey opening saw chances at a premium as the game threatened to be strangled by a midfield stalemate, with a Jake Buxton header and a Kei Kamara effort – both clearing the crossbar – the only chances of note in the opening 25 minutes.
Will Hughes and Craig Bryson harried and probed to try and find Derby an opening, but the audible groans from the home faithful when the latter curled a free-kick five yards over summed up the spectacle so far.
Kamara attempted an audacious bicycle kick that dropped not too far wide of Lee Grant’s left-hand upright as Boro created a rare opportunity, but the pendulum swung Derby’s way after 33 minutes when Boro striker Main left his foot in on Rams defender Buxton and was shown a second yellow card.
The best moment of the half came courtesy of Boro five minutes before the break, shortly after Bryson had tested on-loan Shay Given in the visiting goal, when the lively Albert Adomah skipped past several challenges and burst into the box.
Grant was, however, equal to his well-struck shot.
In first-half stoppage-time, the Rams gained the initiative when Bryson’s sizzling low cross was prodded in by the sprawling Martin.
Boro head coach Aitor Karanka sent on Carayol for Jacob Butterfield at the break, while Jeff Hendrick replaced Eustace as McClaren also made a change for Derby.
Some nice pieces of trickery from Simon Dawkins on the edge of the area then saw him square a ball to Ward, whose driven effort was blocked by Given’s legs.
With 17 minutes to go, Boro were back on level terms and it was all thanks to Carayol’s artistry.
Superbly winning the ball just by the halfway line, he ran the length of Derby’s half and cut the ball back to Rhys Williams.
His effort was blocked but kindly fell to Whitehead who rammed the ball into the bottom corner for his first Boro goal.
Derby struggled to muster a response, but pinched it at the death when Sammon got onto a bouncing ball to beat the stranded Given and break Boro’s gritty rearguard action.
Derby County: Grant, Wisdom, Forsyth, Eustace (Hendrick 45), Keogh, Buxton, Bryson (Sammon 79), Hughes, Martin, Dawkins (Russell 76), Ward
Subs (not used): Bennett, Legzdins, Cissé, Keane
Middlesbrough: Given, Williams Booked, Friend (Ayala 92), Butterfield (Carayol 45), Woodgate, Gibson, Adomah (Varga 87), Whitehead, Main (Dismissed after an earlier booking), Smallwood, Kamara
Subs (not used): Richardson, Emnes, Ledesma, Konstantopoulos
Ref: Andy Madley