Boss Steve Evans brought up a century in style as Rotherham saw off League 1 Play-Off rivals Peterborough United courtesy of a controversial penalty - but he warned his players they have achieved nothing yet.
Kieran Agard earned and converted the decisive spot-kick as the Millers stretched their unbeaten run to 13 matches at London Road in their manager's 100th match at the helm.
One-time Posh loanee Agard went down under a challenge from Ben Nugent in first-half stoppage time.
Already-booked Nugent escaped a second caution, but Posh were still punished as Agard dusted himself down to roll his 18th goal of the campaign past goalkeeper Bobby Olejnik to help Rotherham climb to fourth in the table.
Evans said: "This goes down as a big victory against a very good team, which arrived thanks to a terrific away performance.
"Kieran is adamant there was some contact which makes it a penalty kick and taking that into account you have to be a bit disappointed not to see a second yellow card.
"Peterborough's goalkeeper kept them in the game with a big save in the second half and our goalkeeper has made a couple of his own. When that happens and we win 1-0, he gets a little kiss from me when he walks into the dressing room!
"We have to remember nothing has been achieved yet and it is a case of continuing to work hard and making sure we get the play-off place we all want.
"I have no doubt that if we finish above Peterborough we will be in there."
That certainly looks likely after they powered 11 points clear of their victims.
They were denied a second goal on the hour by a fine save as Olejnik thwarted Nicky Adams in a one-on-one situation following a delightful pass from Ben Pringle.
Rotherham keeper Adam Collin produced super saves in both halves as his team boosted the best away record in League One.
He kept out Nicky Ajose's glorious opportunity in the opening period and then dashed from line to deny Conor Washington at point-blank range midway through the second half.
Posh remain in possession of the final play-off spot but boss Darren Ferguson was left to bemoan the major penalty decision from referee Carl Berry.
He said: "The table doesn't lie at this stage of the season and Rotherham are rightfully in the play-off places, but I thought we were unlucky to lose the game.
"I've seen the penalty incident six times now and it is a poor decision which has had a big bearing on the outcome of a big game.
"We made changes at half-time to try to give ourselves a bit more composure, but we couldn't get a goal and didn't carve out enough good opportunities.
"It is immensely frustrating that we aren't stringing more good results together, but we are giving our fans another roller-coaster ride."