The Millers were up against Wrexham, owned by movie-star duo Ryan Reynolds and Rob McElhenney, and were the better side for much of the contest against the opposition, who had kicked off in second spot.
But they’d conceded in the first minute of the game and that was enough to condemn them to a home loss that ended their four-match unbeaten league run.
The result dropped them a place in the table to 16th.
The Millers fell behind to the first attack of the game as Ryan Barnett crossed from the right and Paul Mullin turned the ball in at the North Stand end despite the attentions of Cameron Humphreys.
Just 16 seconds had gone.
After a shell-shocked first few minutes, the Millers recovered and played their way into the contest.
Joe Rafferty shot just wide when the ball dropped to him in the box and then, in the 23rd minute, the right-back delivered a superb cross that Hakeem Odoffin’s outstretched boot missed by only a whisker.
Wrexham fans had filled the away end and were in loud voice on a sunny autumn day in S60.
With striker Jonson Clarke-Harris missing with a hamstring injury, the Millers had changed shape and were playing Sam Nombe as a lone frontman in a 4-5-1 formation.
On 39 minutes, Joe Powell’s free-kick glanced off the head of a visiting player and it needed a fine scrambling save from Arthur Okonkwo to prevent an own goal before Jamie McCart’s follow-up from an angle was deflected wide.
Referee Ben Atkinson was having a poor game, missing fouls yet blowing for fair challenges, and was perhaps fortunate that home boss Steve Evans was sitting in the stands rather than the dugout as he served a one-match touchline suspension for picking up three yellow cards this season.
Rotherham fans expressed their ire on their manager’s behalf and the official was roundly booed off at the break.
Mullin trooped off with the rest of the Wrexham players, happy to still be involved in proceedings after being only cautioned for a calculated late challenge on Cameron Dawson.
Liam Kelly was back in the matchday squad for the first time since September 7 when he damaged his hamstring at Charlton Athletic.
However, there was still no place for Sean Raggett, who was missing for a sixth successive match, despite Evans saying during the week that he was available for selection.
New York old boy Ollie Rathbone, who came on to a warm ovation from home supporters in the second half, and former loanee Seb Revan were on the bench for the visitors.
The Millers continued to go in search of a leveller at the start of the second half.
Mallik Wilks did the hard work by beating his man but then fired into the side-netting from an improbable angle when he should have crossed.
Soon afterwards, Odoffin headed over the bar before substitute Jack Holmes set up Wilks, whose shot was heading in until Eoghan O’Connell got himself in the way.
At the other end, a weaving run from Barnett resulted in a James McLean effort being deflected and from the ensuing corner, Dawson clung on to Dan Scarr’s header.
A mishit Holmes shot landed kindly for Nombe but his shot on the turn went just the wrong side of the post.
As the clock began to tick down, Rotherham remained on the attack, yet it was Dawson who was the keeper next called into action as he went full stretch to deny Mullin a second goal.
Okonkwo dived to parry a Cohen Bramall free-kick as Rotherham maintained the pressure and the visitors hung on.
So, the Hollywood club went home with all three points, leaving the home side frustratingly empty-handed.
Not the plotline the Millers deserved.
Rotherham United (4-5-1):Â Cameron Dawson; Joe Rafferty, Cameron Dawson, Jamie McCart, Reece James (Jack Holmes 56); Mallik Wilks (Jordan Hugill 78), Hakeem Odoffin (Joe Hungbo 70), Christ Tiehi, Joe Powell, Cohen Bramall; Sam Nombe. Subs not used: Dillon Phillips, Liam Kelly, Alex MacDonald, Shaun McWilliams.
Wrexham (3-5-2):Â Arthur Okonkwo; Eoghan O’Connell, Dan Scarr, Tom O’Connor; Ryan Barnett, Andy Cannon (Ollie Rathbone 62), George Dobson, Elliot Lee, James McLean; Ollie Palmer (Steven Fletcher 70), Paul Mullin. Subs not used: Callum Burton, Lewis Brunt, Luke Bolton, Mo Faal, Seb Revan.
Goals:Â Mullin 1 (Wrexham).
Referee:Â Ben Atkinson (London).
Attendance:Â 11,235 (2,356).