Michael Ihiekwe, Michael Smith and Ryan Giles struck goals in the final quarter of an hour as Wayne Rooney’s side, which had conceded three goals in their past 11 league matches, collapsed spectacularly in a dozen minutes.
While a priceless result for Rotherham, who have two matches in hand on their nearest rivals, it is a setback for Derby who are now one of the sides directly in their line of fire at the bottom.
The match was being played at the third attempt, with the initial attempt in December postponed before kick-off due to a Covid-19 case in the Millers camp and the rescheduled fixture pushed back 24 hours due to a waterlogged pitch.
Story of the match
Despite the postponements, the sides had still met each other recently with Rotherham snatching a late 1-0 win at Pride Park. Derby had dominated possession without making use of it in that game, and it was the same story again in the reverse.
Their struggles in breaking down a resilient and focused and defence continued and they were often reduced to sending long balls into the forwards. Their only real chance of the first half came from a set piece, as Colin Kazim-Richards flicked on a corner for the recalled Martyn Waghorn to attempt an overhead kick, but it fell wide.
Rotherham picked their moments to press and counter, and posed a real threat just before the break. David Marshall had to be at full stretch to deny Smith’s effort from range, before being relieved to see Clark Robertson head over a Dan Barlaser corner from the middle of the six-yard box and Jamie Lindsay smash wide from a Matt Crooks pass over the top.
Viktor Johansson was finally forced into his first real save shortly after the break, the home goalkeeper denying Max Bird’s unconvincing effort, while Matt Olosunde failed to make the most of the Millers’ best break of an uneventful restart when a cross-cum-shot was claimed by Marshall, moments after Graeme Shinnie was fortunate to only receive yellow for a nasty challenge on Crooks.
The second half brought debuts for late January signings who would not have been able to play had the game gone ahead a day earlier, and one of them, Derby’s Lee Gregory, should have got off the mark for his new side within a minute of coming on, only to glance Nathan Byrne’s cross wide.
Three minutes later, they were behind. Giles’ ball took a flick off Smith which took the whole visiting defence out of the picture, leaving defender Ihiekwe barely able to believe his luck as he was left the task of knocking the ball past Marshall for the lead.
There was at least more time for Derby to mount a fightback than in the home fixture, when Lindsay won it at the death, but they could wave away any hopes of that within five minutes. Smith was this time the scorer, applying a deft touch to a fizzing cross from forward partner-in-crime Crooks.
And the late rout was completed when Wolverhampton Wanderers loanee Giles made it two goals in three matches for the club by pouncing on a loose ball, rounding the defence and firing a composed finish beyond Marshall and into the far corner.
Man of the match: Michael Smith (Rotherham United)
Smith has established himself as comfortable first-choice striker and combined a sixth goal in eight matches with brilliant all-round play, as his partnership with Crooks goes from strength to strength.