The Millers, who were relegated at the start of the month, made it two games without defeat after a 1-1 draw at Preston which doubled their away points tally for the season and followed victory over Ipswich.
Richie Smallwood put Warne’s men ahead before Stevie May levelled for North End just before the break.
It has been a season to forget for the Millers, who have gone through an entire away campaign without winning for just the second time in their history. Their only other draw came at Ipswich.
But, in taking five points from the last four games, Warne is encouraged for League One next season. “The lads stuck to the game plan really well, we defended resolutely to the last minute,” he said.
“Back to front I thought we were great. We got on top with a great goal from Richie and their goal was a wonder strike and that is what it has taken to get past us.
“We were tight all over the pitch, so I am happy. A few games ago I told the lads to use this as a mini-season and I think their standards in all of those games has been excellent.
“I am pretty proud of what the lads have put in and I think there are green shoots for next season, so I am a proud manager.
“At least the fans can see they are proud to wear the shirt.”
Preston North End: Maxwell, Browning, Baptiste, Huntington, Spurr, Barkhuizen (Horgan 65), Johnson, Browne, McGeady, Hugill (Makienok 81), May (Robinson 65). Unused substitutes: Lindegaard, Vermijl, Pringle, Andrew Boyle.
Rotherham: O’Donnell, Fisher, Ajayi, Wood (Belaid 87), Mattock, Frecklington (Yates 80), Smallwood, Vaulks, Taylor, Adeyemi, Clarke-Harris (Morris 73). Unused substitutes: Bray, Purrington, Warren, Bilboe.
Referee: R Jones (Merseyside).