West Brom were the beneficiaries of a terrible offside decision as they moved above Liverpool into seventh place in the Premier League after coming from behind to inflict a 2-1 defeat on Swansea City.
The League Cup winners took the lead through Luke Moore, making his first league start of the season, but Michael Laudrup's side allowed the game to slip away from their grasp, surrendering their record of having dropped only two points from winning positions all season.
Romelu Lukaku helped spearhead the recovery, scoring with a fine finish after 40 minutes, but the Belgian striker missed a penalty in the second half, with West Brom getting lucky when Jonathan De Guzman accidentally turned the ball into his own net.
Swansea then appeared to have equalised after 87 minutes when substitute Roland Lamah tucked away his first for the club, but referee Lee Mason followed the advice of his assistant and disallowed the goal for offside. The officials wrongly believed a Swansea player had touched the ball to Lamah, but it clearly came off the boot of Jonas Olsson.
Thanks to their good fortune, West Brom move three points ahead of Saturday's opponents and are now only two points behind sixth-placed Everton, albeit having played a game more.
After scoring the winning goal in a 1-0 win over Newcastle last weekend, Moore started for Swansea, who were without Leon Britton due to injury. West Brom, meanwhile, brought captain Chris Brunt and top scorer Lukaku into the starting XI after they missed the 1-0 defeat to Chelsea.
The changes should have given West Brom more authority but initially they wilted in the face of Swansea's superior passing game, with Michu as animated as ever. The Spaniard was withdrawn in support of Moore, with Pablo Hernandez and Wayne Routledge patrolling either side. And the wingers were involved in the first chance of the game, exchanging passes before Michu poked the ball over the bar at full stretch.
Michu, searching for his 20th goal of the season, was presented with an even better chance after 20 minutes when Swansea broke from the edge of their box with style and worked the ball to Moore with some fantastic first-touch football. He played in Michu but with Ben Foster advancing from his line the prolific Spaniard could only poke the ball just wide of the post.
West Brom were restricted to optimistic long-range attempts from Graham Dorrans and one effort from Brunt that flashed over the bar following a lovely chipped pass from Lukaku, and after 33 minutes they deservedly went behind. De Guzman delivered a corner from the left and Moore stepped away from Claudio Yacob to direct a clever header past Foster from eight yards out.
But Swansea could not press home their advantage and, crucially, could not suppress Lukaku. After 40 minutes the visitors failed to deal with a long ball into the right channel from Foster and allowed Dorrans to pick out the on-loan Belgian, who beat Vorm at his near post with a sweeping, low first-time finish.
The lively Lukaku almost inflicted further damage in first half stoppage time but his clever scooped pass over the defence was met by a volley from Brunt that arrowed straight at Vorm.
The game appeared to be bending to Lukaku's will, but after 57 minutes he passed up a big, big chance to put West Brom into the lead. Routledge tripped Billy Jones outside the box and then, with advantage being played, also made contact with Morrison, who went to ground. Lukaku looked confident enough but struck his spot-kick far too close to Vorm.
Still, the momentum was all West Brom's and on 61 minutes they took the lead. Gareth McAuley rose to meet a corner from the right and though Angel Rangel headed his attempt off the line, the ball caught the shoulder of De Guzman and flew back in for an own goal.
Swansea were lacking the energy that had characterised their performance in the first 30 minutes and Michu's struggles continued as he pinged a shot well over the bar from 15 yards after substitute Nathan Dyer touched a cross back down into his path. Then, with three minutes remaining, the visitors were denied in controversial circumstances.
Lamah tried to play a low cross after breaking clear down the right but Olsson touched the ball back into his path, allowing the winger to slot the ball past Foster from a tight angle. The assistant deemed that Itay Shechter had played the ball to Lamah, who was in an offside position at the time, but it was all Olsson, meaning the goal was legitimate.
Swansea were rightly furious, their protestations continuing after the final whistle as they were condemned to a controversial defeat.
MAN OF THE MATCH
Romelu Lukaku (West Brom): Okay, so he had a penalty saved, but the striker was the most persistent threat and the best of a bad bunch.
WEST BROM: Foster 6, Jones 7, McAuley 7, Olsson 6, Ridgewell 6, Mulumbu 6, Yacob 7, Morrison 7, Brunt 6, Dorrans 5, Lukaku 7. Subs: Odemwingie 6, Thomas N/A, Fortune N/A.
SWANSEA: Vorm 7, Rangel 7, Monk 5, Williams 6, Davies 6, De Guzman 6, Ki 6, Pablo 5, Michu 5, Routledge 6, Moore 7. Subs: Dyer 6, Lamah 7, Shechter 6.