They were not at their scintillating best, but their mean defence, propped up by an excellent goalkeeper, held firm and the division’s leading striker produced an important finish to win the game.
They are also nine points clear of MK Dons, with a game in hand on Tuesday, meaning that if they beat the Dons next Saturday they will have a 15-point cushion and the champagne would firmly be on ice.
There were two champagne moments at Home Park as the Millers won again.
After an open first half, where both sides had chances and Plymouth hit the post, Rotherham took the lead midway through the second half when Michael Smith struck his 18th league goal of the season.
The striker, who looks set to leave in the summer, fired low into the bottom corner after being played through by Ben Wiles.
Then came another big moment as goalkeeper Josh Vickers continued his excellent form by denying Ryan Hardie with a big save 12 minutes from time.
It was another decisive step towards the goal of promotion.
Boss Warne said: “I thought it was a game that both teams were trying to score. I know it is an obvious thing to say but neither team sat behind the ball and the scoreline could have been anything.
“It is a weird one that it was only 1-0. We should have scored more goals as should they have. At times we didn’t defend as I would have liked. But going forward I thought we were OK.
“It all came together in the end, but it didn’t feel like that on the side of the pitch at times. It felt like we were pressing the self-destruct button a couple of times.
“I really appreciate the fans who made a massive effort to come, it is a really friendly club.”