Jarrod Bowen and Fraizer Campbell, with their 16th and 10th goals of the season respectively, fired the Tigers into a 2-0 half-time lead at the KCOM Stadium.
But Millers boss Paul Warne changed the game with his substitutions, bringing on Anthony Forde and Jon Taylor.
Forde gave Rotherham hope by pouncing on a mistake from David Marshall following good work from Taylor, who then saw his shot deflected in to level the scores in the 55th minute.
Defender Clark Robertson, passed fit following an ankle injury, had headed a long Joe Mattock free-kick well wide for Rotherham in the opening minute.
Yet the Millers' chances of ending their 40-game winless streak on the road in the second tier appeared to go up in smoke just a minute later.
A delightful through ball from Evandro pierced the visiting defence, allowing Bowen time and space to fire right-footed across Marek Rodak and into the far corner.
Hull were oozing confidence and a deserved second goal arrived in the 23rd minute through Campbell, who bundled home Kamil Grosicki's cross from close range.
Tigers goalkeeper Marshall had to be alert to parry a Richie Towell snapshot, but normal service resumed soon after for the hosts.
Rodak was forced to scramble back to claw out a Grosicki cross that caught him off guard before Jackson Irvine curled an ambitious effort from distance over the top.
Warne attempted to turn the tide in the 38th minute, replacing Jerry Yates with Forde, and Will Vaulks almost gave him an instant response.
The midfielder stung the palms of Marshall with a 25-yard piledriver to hand the Millers, second best in all aspects, some encouragement.
Warne then introduced Taylor and his side responded by scoring twice in the first 10 minutes of the second half.
Having advanced down the right wing, Taylor delivered a cross that Marshall spilled into the path of Forde, who tapped into the empty net in the 48th minute.
Then, seven minutes later, Marshall could do nothing to keep out a Taylor shot that took a huge deflection off Robbie McKenzie and nestled in the bottom corner.
Suddenly, Rotherham were in control and Marshall was forced to tip over headers from Robertson and Michael Ihiekwe.
Hull were rattled, incensing the home fans with their sloppy play, although Grosicki's volley almost squirmed through Rodak's hands.
Vaulks scuffed a shot wide late on for Rotherham while Irvine headed off target unmarked for Hull.