A goal either side of half-time looked to have secured the points for Neil Warnock's side, but the battling Millers showed their team spirit is still intact - despite their position at the foot of the Coca-Cola Championship table - as they fought their way back to 2-2.
The visitors went ahead with goals from Michael Tonge and Paul Shaw, but the Millers responded with headed goals from defenders Martin McIntosh and Chris Swailes to earn a much-needed point for Ronnie Moore's side.
The first half was packed full of incident with plenty of chances before Tonge eventually struck.
Jamal Campbell-Ryce created space down the left in the second minute and whipped in a quality ball but Paul McLaren was unable to direct his header on target.
Campbell-Ryce was again involved after 11 minutes when a brilliant piece of skill took him past his marker before putting in a pin-point cross only for Junior to head wide.
The home side were hampered after 19 minutes when Shaun Barker was forced off with a knee injury to be replaced by Paolo Vernazza.
The Blades 'keeper Ian Bennett - making his debut after signing on loan from Birmingham - was involved in a horrendous clash with Millers striker Martin Butler.
Bennett came out to meet a long ball which Butler was chasing and the two men collided, with the striker coming off worst and having to be carried off on a stretcher. He was later taken to hospital with concussion.
Two minutes later Junior was played through by McLaren but spurned a gilt-edged chance to nudge Ronnie Moore's men in front.
Andy Gray missed another chance for the Blades shortly before half-time when Mike Pollitt denied him after he had scuffed his first effort.
The Blades finally struck six minutes into first-half injury time when Tonge made a great run down the left and finished well to leave the Millmoor faithful in stunned silence.
Shaw made it 2-0 to the visitors immediately after the half-time break. The 31-year-old former Millers player took advantage of some lazy Rotherham defending to force the ball past the despairing Pollitt.
Sheffield United looked like they had gone 3-0 up in the 53rd minute but the referee's assistant judged that Gray was offside and Tonge's effort was disallowed.
Rotherham forced their way back into the game immediately afterwards when Swailes rose to meet an inch-perfect free-kick from McLaren, and powered his header past Bennett into the bottom corner.
The Millers should have got back on level terms when Campbell-Ryce played a magnificent ball through to McLaren but he was denied by the sprawling Bennett. Junior was unable to score from the rebound.
Rotherham deservedly equalised in the 71st minute when McIntosh met McLaren's corner and glanced a fine header over Bennett's outstretched arms.
Blades' substitute Danny Cadamarteri had a fine chance to put his side ahead in the 80th minute but Pollitt produced another fine save to deny the former Everton striker.
The home side forced some late pressure but were unable to score the winner, with Junior spurning yet another chance in the dying minutes.