ROTHERHAM UNITED are destined for a return to League One after late goals from Jay Rodriguez (penalty) and Rakeem Harper saw West Brom triumph at the Hawthorns.
Hopes of a Great Escape were still on when Clark Robertson put the Millers ahead early in the second half with a header.
But Albion stepped up a gear after the setback to run out winners, with Millwall’s point in the early kick-off against Stoke meaning that Rotherham now return to third tier from whence they came just under 12 months ago.
The Millers had the better of a scrappy first half, with the hunger and desire on show almost exclusively arriving from those in visiting jerseys.
Albion, by contrast, looked a side who were very much waiting for the play-offs, with their fate in the top-six assured - although though the hosts were supposedly playing for position and ensuring that they would be playing the second leg of their semi-final on home soil.
You would not have noticed given a meek first-half performance, with the Millers producing some nice pockets of play and comfortably having the better of proceedings.
With Millwall’s draw effectively meaning that Warne’s side had to win to keep their outside chance of survival alive, the onus was on the Millers and they produced the dangerous moments on offering in the first period.
Their best moment arrived on 17 minutes when the recalled Clark Robertson saw his header hit the woodwork from a well-directed Joe Newell corner.
Semi Ajayi glanced a header wide, while United also went close before the interval when Kyle Bartley’s clearance following Will Vaulks’s long throw was cleared on his own goaline by Craig Dawson.
After bringing next to nothing to the table in the first period, Albion could have been expecting a few harsh words at the interval from caretaker-boss James Shan.
Things then got worse for Albion - jeered off by some supporters at the break - on the restart and they could have few complaints at going behind.
The vital moment arrived when Robertson arose highest to Newell’s excellent centre, with his header deemed as having gone over the line, despite the best efforts of Chris Brunt to clear.
The goal was no more than the visitors deserved, although it was the cue to a belated response from the hosts.
Top-scorer Dwight Gayle, hitherto quiet, scuffed an opportunity after Ahmed Hegazi headed on a corner from Chris Brunt, with his reaction suggesting he should have done better.
Albion then contrived to produce their best chance of the game with the Millers afforded a let-off when Mason Holgate blazed over when well placed after latching onto a dangerous left-wing cross from substitute Matt Phillips.
Marek Rodak was then called into action to tip over Holgate’s lob after the defender was left unmarked following Brunt’s free-kick.
The hosts were then afforded a lifeline from the spot after Gayle tumbled under pressure from Michael Smith and Rodriguez was not about to pass up such a gift, confidently sending Rodak the wrong way to put Albion level.
Soon after, the Millers were facing a mountain to climb after home pressure saw the ball break for Harper, whose unstoppable low drive flew past Rodak.
Substitute Kyle Vassell went close to levelling, but the Millers’ fate was unfortunately sealed, despite a brave performance and season.
Phillips and Robson-Kanu went close to sealing it before Newell’s effort shuddered the woodwork - the prelude to the final whistle and end of Rotherham’s Championship stint.
West Brom: Johnstone; Dawson, Bartley, Hegazi; Holgate (Murphy 78), Harper, Brunt, Gibbs, Johansen (Phillips 67); Rodriguez (Robson-Kanu 86), Gayle. Substitutes unused: Bond, Adarabioyo, Townsend, Field..
Rotherham United: Rodak; Jones (Vassell 82), Ihiekwe, Robertson, Mattock; Ajayi; Forde (Williams 82), Vaulks (Towell 72), Crooks, Newell; Smith. Substitutes unused: Price, Wood, Taylor.
Referee: R Jones (Merseyside).