The Millers chief used the hosts' pre-game boasts in their matchday programme about how they were the best side in League One, plus the fact that his team found themselves locked out of the Kassam Stadium upon their arrival as motivation ahead of kick-off.
The result was a superb first-half display that saw Rotherham score three unanswered goals, paving the way for a 3-1 success which took them to the top of the table.
The contrast betweent that performance and the one that United served up during the opening 45 minutes of Saturday's home clash with Bristol Rovers was stark.
Comfortable though they were for the most part, the Millers never really got out of second gear, and could easily have found themselves a goal down inside three minutes.
On this occasion, it was what Warne said to his charges inside the dressing room at the interval, rather than before the first whistle, that was to prove critical.
Whatever it was that he did relay during that half-time address, it certainly worked.
Far too pedestrian in the first period, Rotherham came out and showed that they meant business after the resumption, netting twice in the space of as many minutes to decide the contest and ensure that they remain in pole position.
Things could've panned out very differently had Rovers striker Jonson Clarke-Harris not spurned a glorious early chance to open the scoring against his old club, missing the target when he was picked out by Alex Rodman's inviting right-wing cross.
The closest the Millers came at the other end was when Michael Smith met Ben Wiles' centre from the left, but got too much on his header.
The hosts continued to deliver some threatening balls into the away box, however that was about as good as it got for them during a tepid opening half.
Clarke-Harris drew an important, diving stop out of United custodian Daniel Iversen on 34 minutes, though there was little real action of note before the break.
But, just five minutes after the resumption, Rotherham moved in front courtesy of Kyle Vassell's fourth goal in three matches.
Chiedozie Ogbene delivered a perfect cross from the right and the in-form ex-Blackpool striker headed past the horribly exposed Jordi van Stappershoef from close range.
Less than 120 seconds later, Ogbene produced another excellent centre and this time it was Michael Smith who rose to nod into the bottom right-hand corner of the net.
And that was pretty much that as far as the game as a contest was concerned.
United continued to look a threat when they went forwards, while it took until the final 10 minutes for Rovers to muster any kind of a meaningful response.
Josh Ginnelly’s headed effort was tipped over the cross-bar by Iversen, then Clarke-Harris went close again, nodding narrowly the wrong side of the upright.
But, the result was put well and truly beyond doubt two minutes from time when Ogbene progressed from prodvider to finisher.
Substitute Freddie Ladapo demonstrated some nice footwork as he cut inside off the left and drew a sprawling parry out of Stappershoef, however the Millers' man of the match was on hand to clinically sweep home the loose ball, wrapping up three points for his side.