The Millers were trailing at half-time to Mirco Antenucci’s effort, but they put in a barnstorming performance after the restart and turned it around thanks to goals from Alex Revell and substitute Jonson Clarke-Harris in the space of seven minutes.
It recorded just a second league win over their illustrious opponents since 1962 and, after taking seven points from games with Blackburn, Norwich and United, showed they are a force to be reckoned with in the Sky Bet Championship.
Milanic can only dream of such a points haul as he is still waiting for a first win in charge of Leeds after four games and, with an owner with the track record of Massimo Cellino, he is still to convince the Italian he is the right man for the job.
Despite a red-hot pre-match atmosphere, the game took a while to get going, with the only moment of note in the opening 15 minutes coming when Antenucci screwed an effort wide after an inventive run by Alex Mowatt.
The Millers then had a fine chance to go a head midway through the first half.
Revell took advantage of Leeds skipper Jason Pearce being laid out injury and slipped Matt Derbyshire in, but the former Blackburn striker drove straight at Marco Silvestri from the edge of the area.
That incident spiced the game up and, after a goalmouth scramble almost allowed Rotherham to take the lead, it was Leeds that went ahead on the half-hour.
Souleymane Doukara broke forward and slipped in Antenucci, who beat the offside trap and finished calmly into the bottom corner for his third goal for the club.
The visitors had Silvestri to thank for keeping their lead in tact as the Italian goalkeeper made a superb stretching save to keep out Revell’s header from a superb Ben Pringle cross.
It was an open game and Leeds had a golden chance to double their advantage on the stroke of half-time but a superb last-ditch tackle from Joe Skarz denied Doukara, who then kicked fresh air with the rebound.
It was clear manager Steve Evans had got into his men at half-time as they came out firing after the break and Silvestri was tested again when he had to beat away Paul Taylor’s wicked free-kick.
Leeds could not survive the onslaught for much longer, though, and the Millers deservedly drew level in the 58th minute.
Lee Frecklington surged into the penalty box and forced Silvestri into another save, but this time the rebound fell kindly and Revell was on hand to ram home his first goal since his double at Wembley in the League One play-off final last season.
There was no stopping a rampant Rotherham and they forged ahead with a moment of brilliance from Clarke-Harris seven minutes later when the striker powered an unstoppable 25-yard drive into the bottom corner with virtually his first touch.
It was the 20-year-old’s first goal since joining the club and highlighted exactly why the Millers paid #400,000 for his services on transfer deadline day.
The Millers’ bombardment eventually began to run out of steam and Leeds came back into it as they looked for an equaliser.
Brazilian striker Adryan, making his eagerly anticipated debut, twice went close with efforts from distance, the first forcing Adam Collin into a fine fingertip save.
Milanic’s men continued to turn the screw and Collin again made a smart low save, turning Antenucci’s effort onto the post and wide.
Revell wasted two chances at the death to put the finishing touches on the win, but the hosts held on for a long-awaited win over Leeds.