Leeds scored early in the second half to take command of the first leg at Pride Park.
Kemar Roofe’s fine finish sent Leeds fans into raptures as Derby struggled desperately to get back into the game.
And with 13 minutes left, Derby thought they had found their route back into contention when they were awarded a penalty.
Leeds Jack Harrison was adjudged to have fouled Derby’s Jayden Bogle in the area as the right-back got through on goal.
But after referee Craig Pawson made his decision, the linesman decided to give his two cents, ultimately changing Pawson’s mind.
The decision was overturned and given as a Leeds free-kick.
And Leeds fans are absolutely loving it on Twitter…
One said: “guess it evens out from the dive from Lawrence in Sunday hahahaha waaaayyy.”
Another went with: “Hahahahahaha imagine thinking that was a penalty.”
A third wrote: “Wasn’t a penalty. Leeds player got pushed if anything.”
One jokingly started a new hashtag, tweeting: “#stoptheflop.”
One angry Derby fan chimed in, however, with: “Just shows Leeds cheating dirty gits fall at slightest touch bogle hardly touched him.”
One found the situation hilarious, tweeting: “Derby hahahahahahahhahah.”
Another Derby fan couldn’t believe the decision reversal, writing: “Wtf kind of decision is that! Injustice.”
Marcelo Bielsa’s Leeds play their second leg with Derby on Wednesday at Elland Road.