United fans are enjoying the unfamiliar feeling of entering a new year with something to play for and they maintained their momentum thanks to Kyle Bartley's header and Chris Wood's double in the second half.
Although not at their best - particularly in the first half - Leeds turned on the style after the break as they moved up to fourth in the table and maintained dreams of a promotion push in the second half of the season.
Rotherham look to be leaving the division in May - through the trapdoor. The hapless South Yorkshire club could not capitalise on a strong opening 45 minutes and slipped to a 17th defeat of the season, leaving them 12 points adrift of safety.
Garry Monk's men would have seen this clash as a real opportunity to begin 2017 well but it was Rotherham who enjoyed the best early openings.
Anthony Forde tested Rob Green with a curling free-kick which the former England goalkeeper could only palm away to Tom Adeyemi, whose rebound crashed into the post from an acute angle.
Leeds began to control the majority of possession but they did little with it and it was the Millers who continued to present the bigger goal threat.
Some good work down the right saw Darnell Fisher pull the ball back to Izzy Brown but the Chelsea loanee wasted a superb chance when he fizzed over the bar from 10 yards.
Leeds were then reliant on the masterful Bartley to twice rescue them.
First the centre-half made a brilliant last-ditch tackle to stop Joe Newell getting through on goal and then he blocked Kirk Broadfoot's header.
The home crowd, who had sold out, were unhappy at half-time but they would have taken comfort from the knowledge their side could not be as bad after the break and they needed only three minutes to prove it.
Leeds forced an early corner and Bartley found himself unmarked at the far post, where he had no problems powering a header home.
That effectively killed off any hopes Rotherham had and Wood made the game safe for Leeds with a superb goal midway through the second half.
The striker controlled Liam Bridcutt's cross with his chest, held off Broadfoot's challenge and then fired in an unstoppable effort into the roof of the net.
The hosts were beginning to enjoy themselves and Gaetano Berardi hit the post with a low effort before Wood added his second with a sweeping finish from close range 11 minutes from time.
It was almost four at the end but Pablo Hernandez rattled the woodwork with a low free-kick - but by then more than 33,000 Leeds fans were already celebrating a winning end to a productive festive period.