Substitute Freddie Ladapo scored twice in the second half as Rotherham came from 2-0 behind to beat MK Dons.
Millers chief Paul Warne admitted that the introduction of Ladapo and Kyle Vassell were the key to victory.
The hosts led 2-0 at the break through Alex Gilbey and Joe Mason, but goals from Dan Barlaser and Ladapo condemned them to a fifth straight league defeat, made worse when Baily Cargill saw red at the end.
Cargill had dithered in the area to allow Barlaser to tap home in the 66th minute.
The Millers levelled moments later when Vassell’s free-kick was tapped home by Ladapo.
Rotherham were awarded a penalty in the 72nd minute when the Ladapo went to ground but his spot-kick smacked the crossbar.
Ladapo made amends four minutes from time when he nodded home the winner from another Vassell set-piece, before Cargill was sent off for an off-the-ball incident.
After a fourth successive away league victory, Warne said: “Vass and Freddie were a constant thorn when they came on.
“Vass was unbelievable. The lads trust him. He demands a lot from people on the pitch. Everything that was good about us in the second half came through him and he will be really pleased. I’ve been singing his praises for weeks and it was nice to put him on.”
Warne’s side moved up to fourth despite him admitting that his side were far from their best in the opening period.
Milton Keynes Dons: Nicholls, Poole, Walsh, Cargill, Lewington, Houghton, Brittain (Boateng 69), Gilbey, McGrandles (Reeves 76), Bowery (Dickenson 82), Mason. Unused substitutes: Moore, Kasumu, Asonganyi, Sorinola.
Rotherham UNited: Iversen, Olosunde, Ihiekwe, Robertson, Jones, Barlaser, Wiles, Morris, Crooks (Vassell 46), Hastie (Clarke 64), Smith (Ladapo 46). Unused substitutes: Thompson, Price, Lindsay, Lamy.
Referee: R Joyce (Cleveland).