Rotherham missed the chance to move to within a point of safety, as they were beaten 1-0 by play-off bound Brentford in their penultimate game in hand on Tuesday.
The only goal of the game came after 26 minutes at the Brentford Community Stadium, as Bryan Mbeumo - whose goal earned the Bees a 1-0 win over Bournemouth on Saturday - headed Sergi Canos' cross home.
Following their fifth straight defeat, Paul Warne's men stay 22nd in the table, with 39 points from their 43 games so far, and remain four points behind Wayne Rooney's Derby in the relative safety of 21st.
Brentford, meanwhile, lead Bournemouth, Barnsley and Swansea by four points and stay in pole position to finish third with two games to play.
In spite of the fact they were playing their ninth and final game of a punishingly congested April, the Millers made an energetic start in west London. Michael Smith and Richard Wood both headed wide of the right-hand post, while Lewis Wing's free-kick flew across the penalty area crying out for a killer touch that never came.
While the chances were less than clear-cut, the hosts soon punished their opponents. Canos cut in off the left flank, beat Wes Harding and clipped in a delightful cross that Mbeumo glanced past Jamal Blackman for his second goal in as many games.
The Championship's top scorer Ivan Toney had drawn a blank in his previous three games, as the wait to break Glenn Murray's record of 30 in a season continued, and in the dying second of the first half, he chased down Emiliano Marcondes' neat flick and crashed a shot off the right-hand post.
He turned his head in disbelief with an hour on the clock. Mads Roerslev's cross from the right presented him with a free header at goal, albeit from the penalty spot, and though he generated an impressive amount of power, Blackman reacted quickly to bat the ball away from danger.
Later, Millers substitute Kieran Sadlier's thumping shot took a deflection on its way to David Raya's grasp, while at the other end Marcus Forss dallied and dragged a shot wide.
Warne's cries for his players to continue digging in grew increasingly desperate as the time ticked by and though they did follow his orders, there was little threat of a crucial reply as they fell to a familiar defeat by a one-goal margin.