The striker came on shortly before half-time and netted his first goal since January
Jack Marriott breathed new life into Derby’s hopes of reaching the Championship Play-Off final, when he came off the bench and equalised just 33 seconds later with his first touch.
Rams boss Frank Lampard decided to haul off midfielder Duane Holmes and introduce Marriott shortly before half-time in a bid to put Leeds on the back foot in the second leg at Elland Road.
And that substitution proved to be a masterstroke, as the former Peterborough forward capitalised on a defensive mix-up between Liam Cooper and Kiko Casilla to tap into an empty net and make it 1-1 on the night, with his first goal since January.
Despite Derby‘s bright start, it was Leeds who went ahead in the 24th minute, when Stuart Dallas was left to side-foot the ball in, after the rebound had fallen kindly to his feet from a Kelle Roos save.
The situation got even better for Derby, who continued where they left off, by scoring their second just after the break through Chelsea loanee Mason Mount.
They were in dreamland soon after as Harry Wilson held his nerve to send Casilla the wrong way from the penalty spot and give the visitors the lead for the first time in the tie.
But Dallas struck his second and Leeds, with a superb finish after a clinical counter attack from the hosts.