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.
9. Duncan Watmore - 7
Full of energy and was unfortunate to have a goal ruled out for a foul. 7 Photo: Stu Forster
10. Yannick Bolasie - 7
Looked lively throughout. His final ball was a bit erratic but he caused Rotherham problems. 7 Photo: Stu Forster
11. Chuba Akpom - 7
Was more involved than in previous weeks as he dropped deep to receive the ball. Took his goal well. 7 Photo: Jacques Feeney
12. Connor Malley - 8
(for Hall, 24) An excellent senior debut after coming on in the first half. Comfortable on the ball and played some excellent forward passes. 8 Photo: JPI Media