Derby County have booked a place in the Championship playoff final with a remarkable 4-2 victory over Leeds United at Elland Road, recovering from a two-goal aggregate deficit to progress through 4-3 over the two legs.
County boss Frank Lampard brought on Jack Marriott towards the end of the first half, though, and that proved an inspired change as the striker kickstarted his side's comeback following a big error at the back from Kiko Casilla and Liam Cooper.
Mason Mount levelled up the tie less than a minute into the second half and Harry Wilson converted from the spot to complete the comeback, only for Dallas to score his second of the match to make it 3-3 on aggregate, but Marriott won the match five minutes from time after Gaetano Berardi had been shown a red card.
Leeds struggled to cope with Derby's new formation in the opening quarter of the match, yet the only opportunity in that period of the game fell the hosts' way as Luke Ayling volleyed over from Mateusz Klich's cross after making a positive run into the box.
The Whites were in front 24 minutes in when Kalvin Phillips' free kick went right the way through the box, hit the post and Dallas was quickest to react to the rebound four yards out.
Derby, going with a diamond formation in the middle, lost all control of the game for the next 20 minutes as Leeds created a couple of good opportunities.
Klich hit the crossbar with a heavily-deflected effort and Patrick Bamford, earlier booked for trying to con the officials by going to ground in the box, had a tame effort kept out from the edge of the box.
In a flash, though, and after hitting the post through a looping Mason Bennett header, County were back in the game thanks to an inspired substitution from Lampard.
Less than a minute after coming on for Duane Holmes, Marriott profited from a terrible mix-up at the back by converting into an empty net once Cooper and Casilla failed to deal with a simple flick-on, rolling the ball into an unguarded net from his first touch.
Derby scored their second a minute into the second half through Mount, who picked out the far corner of the net despite losing control of the ball and slipping just as he pulled the trigger.
Mount wasted a big chance to double his personal tally three minutes later when denied by the leg of Casilla, while Dallas and Pablo Hernandez were thwarted by Kelle Roos and Fikayo Tomori respectively in the space of 10 seconds.
The game became incredibly open and the fourth goal of the night fell the Rams' way as Bennett played a one-two with Tom Lawrence and was dragged back by Cooper, allowing Wilson to convert from the penalty spot.
Leeds showed great character by responding four minutes later through Dallas's curled finish into the bottom corner following a nice touch into his path from Klich, though replays show the goalscorer was offside.
United looked the more likely side to score a winner before full time, but they lost Berardi to two red cards - the second yellow coming after a poor challenge on Bradley Johnson - and that once again changed the complexion of the tie.
Lampard's men instead went in search of a winner and they found it when Marriott took Richard Keogh's pass in his stride and lifted the ball over Casilla, shortly after Wilson had picked out the post with his caressed finish.
Leeds had a couple of half-chances in the remaining 10 minutes, while Malone was sent off for a second bookable offence, but County held on to become the first side ever to lose the first leg of a Championship playoff semi-final on home soil and still progress through.
LEEDS UNITED (4-5-1): Casilla; Ayling, Berardi, Cooper, Dallas; Hernandez, Shackleton, Phillips, Klich (Clarke 86'), Harrison; Bamford (Brown 88')
DERBY COUNTY (4-2-3-1): Roos; Bogle, Keogh, Tomori, Malone; Holmes (Marriott 44'), Johnson; Wilson (Cole 93'), Mount, Lawrence; Bennett (Huddlestone 59')