Boro had endured a five-game winless run ahead of their trip to the New York Stadium and made a terrible start when Angus MacDonald headed the hosts ahead from a corner.
Yet Boro took control when Rotherham’s Matt Crooks was sent off midway through the first half following a collision with Grant Hall.
The visitors then drew level when George Saville fired the ball home from a short corner, before Chuba Akpom scored his first goal since January to put his side ahead in the second half.
Boro also handed a debut to midfielder Connor Malley, who replaced Hall and impressed with his range of forward passing.
Fulham loanee Neeskens Kebano was also a constant threat for Warnock’s side.
Here’s how the Teessiders fared at the New York Stadium.
5. Marvin Johnson - 7
Delivered some inviting crosses from the left, including a free-kick which led to the second goal. 7 Photo: George Wood
6. Jonny Howson - 8
Forced to drop back into defence and swept up danger. Hit the bar with two efforts. 8 Photo: Stu Forster
7. George Saville - 7
Drew his side level with an emphatic finish. Comfortable in midfield against 10 men. 7 Photo: Stu Forster
8. Neeskens Kebano - 8
Boro’s best on the evening. A constant threat as he drew defenders and created chances for his team-mates. 8 Photo: Getty Images