Albion will face Aston Villa in the Sky Bet Championship Play-Off semi-finals after being defeat 3-1 by Derby County at Pride Park.
The Rams went in front through Martyn Waghorn’s header and held their lead until two minutes after half-time, Stefan Johansen finishing off a great move for the Baggies.
However Frank Lampard’s side, knowing a win would secure sixth in the table and a place in the Play-Offs, netted twice in a matter of minutes through Mason Bennett and Harry Wilson to take the spoils in Derbyshire.
Derby will face Leeds United for a place at Wembley whilst Albion look to get through a Midlands derby, with both first legs taking place next Saturday.
James Shan made just one change to the side that beat Rotherham last weekend with Jacob Murphy coming in for Chris Brunt.
And it was Albion who started strongly, finding themselves unfortunate not to go ahead early on when Murphy, played through by Jay Rodriguez, saw an effort go just wide.
But after 19 minutes it was Derby who grabbed the opening goal as Waghorn powered a header past Sam Johnstone.
There were chances to equalise before the break for the Baggies. Dwight Gayle poked narrowly past the post when in space inside the area and Ahmed Hegazi headed Johansen’s corner over.
Immediately following the restart Albion did find an equaliser, though. A fantastic build-up saw the ball fall to Johansen on the right-hand side of the box and he made no mistake in smashing home his second for the Club.
Derby piled on the pressure with a Play-Off spot at stake and eventually managed to re-take the lead when substitute Bennett converted a rebound from close-range on 70 minutes.
The home side then won a penalty three minutes later, with Harry Wilson on hand to convert it and extend their advantage further.
As the game went into stoppage time substitute Hal Robson-Kanu received a red card to reduce Albion to 10-men, with referee Tim Robinson bringing the game to an end shortly after.
ALBION: Johnstone, Bartley (Robson-Kanu 78), Dawson, Hegazi; Holgate, Johansen (Field 75), Harper, Gibbs; Murphy (Phillips 60), Gayle, Rodriguez.
Substitutes: Bond, Mears, Townsend, Morrison.