Substitute Jack Marriott was the hero as Derby stunned Leeds to set up a Championship play-off final against Aston Villa after a wild night at Elland Road.
The hosts took the lead on the night to go 2-0 up on aggregate when Stuart Dallas tapped in after Liam Cooper’s header had hit the post.
Marriott levelled with his first touch before half-time after a horrendous mix-up at the back between Cooper and keeper Kiko Casilla.
The Rams turned the tie on its head after the break through Mason Mount and a Harry Wilson penalty, only for Dallas to drift in and fire Leeds back level on aggregate.
Leeds defender Gaetano Berardi was then sent off for a poor challenge on Bradley Johnson before Marriott won it late on with a composed finish.
There was still time for Derby defender Scott Malone to join Berardi in being dismissed after collecting a second booking in time added on.
For Leeds, who finished third in the table, defeat means their spell outside the top flight will stretch to a 16th year.
Derby, meanwhile, become the first team to lose the first leg of a Championship play-off semi-final at home and go on to reach the final.
Rams stage improbable comeback on incredible night
There had been no indication of what would transpire on this crazy night in West Yorkshire when Dallas put Leeds in front.
They had won all three of the previous meetings between the two sides this season by an aggregate of 7-1 and Derby looked short of ideas when they did manage to launch any attacks.
However, with half-time approaching, Rams boss Frank Lampard brought Marriott on for midfielder Duane Holmes and the former Peterborough man had an instant impact, tapping in after Cooper and Casilla ran in to one another to leave him with an open goal.
A brilliant finish from Chelsea loanee Mason Mount put them in front on the night and Harry Wilson, on loan from Liverpool, kept his composure to fire home from the spot after Cooper pulled Mason Bennett’s shirt in the area to put Derby ahead in the tie for the first time and spark wild scenes in the away end.
Leeds responded well and Dallas deservedly pulled one back to draw them level at 3-3 on aggregate with a wonderful finish, but Berardi’s red card shifted the momentum once more and defender Richard Keogh sprinted out of defence to play a measured pass for Marriott to poke in and book the Rams a trip to Wembley on Monday, 27 May.
Leeds fall short again
With four games of the regular season to go, Leeds had been in the driving seat to win automatic promotion after a hugely impressive season under veteran Argentine head coach Marcelo Bielsa.
However, they suffered a shock home defeat by strugglers Wigan on Good Friday before losing at Brentford three days later as their three-point lead over Sheffield United turned into a three-point deficit that they were unable to overturn.
With many fans fearing their moment had passed, they put in an assured performance at Pride Park in the first leg to come into this game with a one goal advantage but, once more, they could not finish the job.
Bielsa reflected that the defeat by Wigan that took their momentum away had been “the decision of God”.
He now faces a huge decision of his own whether to carry on as Leeds boss after a hugely emotional campaign that saw him pay a £200,000 fine after the club were reprimanded for sending a member of staff to watch Derby train before the league game between the teams at Elland Road in January.