The Millers were 3-1 down and the home side had missed a penalty before Paul Warne's men somehow turned round proceedings against Oxford United at the Kassam Stadium.
Ryan Williams struck on the stroke of half-time to keep the visitors in the game and Kieffer Moore's 11th goal of the campaign, in the second half, earned them a point that had seem impossible when the U's were running Rotherham's defence ragged.
The Millers' defending was nowhere near good enough in an opening period which brought five goals and a saved spot-kick.
Joe Newell fired Rotherham into a 20th-minute lead, but the home side levelled a minute later through Jack Payne, before Josh Ruffels added a 30th-minute second.
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Marek Rodak saved a Ryan Ledson penalty, awarded for handball by Will Vaulks, in the 32nd minute, but Ledson redeemed himself by scoring Oxford's third on 40 minutes, stabbing home after a scramble during which Rotherham should have cleared the danger.
After being second best, the Millers found themselves back in the match on the stroke of half-time when Williams finished off Vaulks' long throw, despite suspicions of a Semi Ajayi push in the build-up to the goal.
The second half was more even, with Joe Mattock and Payne trading chances and Moore's lob hitting the bar until the Millers struck in stunning style in the 78th minute.
Newell fed Williams with a great ball and the winger's superb cross from the left found Moore who buried his close-range finish for his 11th goal of the season.
Rodak kept the scores level with a fine save from Joe Rothwell with seven minutes to go but it was Rotherham who finished the game on the front foot and looking the side most likely to win an amazing encounter.
The point keeps the Millers in a play-off spot, in fifth place.
Goals: Payne 21, Ruffels 30, Ledson 40 (Oxford); Newell, 20, Williams 44, Moore 78 (Rotherham).
Oxford (4-2-3-1): Eastwood; Carrroll, Nelson, Mousinho, Ricardinho; Ruffels, Ledson; Henry, Payne, Mowatt (Rothwell 64); Thomas (Obika 78). Subs not used: Shearer, Tiendalli, Williamson, Martin, Fernandez.
Rotherham (4-1-4-1): Rodak; Emmanuel, Ajayi, Ihiekwe, Mattock; Vaulks; Williams, Towell (Taylor 68), Newell, Forde; Moore. Subs not used: O'Donnell, Ball, Clark-Harris, Yates, Cummings, Wood.
Referee: Sebastian Stockbridge (Tyne).
Attendance: 7,471 (608).