West Brom's slim chances of automatic promotion suffered a major blow as Millwall boosted their Championship survival hopes with a 2-0 win.
Ryan Tunnicliffe's first-half strike and an Ahmed Hegazi own goal were enough to earn the home side all three points in a result which moves them to 20th in the table – one point clear of the relegation zone.
But West Brom's problems were largely of their own making, with goalkeeper Sam Johnstone gifting Millwall the first goal and Jay Rodriguez missing a penalty shortly before Hegazi diverted into his own net.
Hegazi completed a terrible day for the Baggies by earning a second yellow card 10 minutes from time.
Millwall were the better side from start to finish and might have gone ahead after 10 minutes, but Lee Gregory fired over from 10 yards after a fine run and cut-back from Ben Thompson.
The home side continued to have the better of things but created very little, until Johnstone's error gifted them the lead after half an hour.
The goal came from nothing, with Tunnicliffe's seemingly harmless shot struck straight at the Baggies goalkeeper. But Johnstone dived past the ball, palming it into his own net.
The strike galvanised Millwall, who could have scored twice more in the next five minutes.
Jake Cooper was denied by Johnstone from a corner, before Mason Holgate cleared Ryan Leonard's follow-up off the line. Moments later Johnstone did well to push away Jed Wallace's curling effort.
West Brom produced almost nothing of note, a Stefan Johansen long-range volley in the 45th minute their only shot on target.
The Baggies should have been level on the hour mark, however. Dwight Gayle got the wrong side of Cooper in the box, the Millwall defender pulling him to the ground to leave referee James Linington with no choice but to award a penalty.
But Rodriguez's spot-kick was dreadful and scuffed wide of David Martin's post.
Six minutes later and it went from bad to worse for West Brom. Thompson danced along the byline and cut the ball into a dangerous area, where it deflected through a crowd of legs, taking the telling touch off Hegazi, and in at the near post.
The visitors never looked like getting back into the game from that point, and in fact it was Millwall who had the better of the late chances, Johnstone saving well from Gregory before Wallace and Thompson both went close.
Hegazi, booked for jumping unfairly in the first half, picked up a second yellow late on for pulling back Gregory.
The result leaves West Brom seven points outside the automatic-promotion spots with six games to play.