THE Hawthorns once again proved a happy hunting ground for Barclays Premier League opposition after the Baggies squandered a 54th-minute lead.
The wintry conditions did not make for the best of spectacles but Albion got their noses in front through the revitalised Marc-Antoine Fortune's second goal in as many home games.
However, the hosts' lead was wiped out within five minutes when Gylfi Sigurdsson levelled and Danny Graham made it 2-1 to the Swans.
Peter Odemwingie missed a great chance to equalise on 71 - before Roy Hodgson's men slumped to an eighth home league defeat of the season.
The two teams were separated by just one place and a point at kick off, as 15th entertained 14th.
Fit-again Jerome Thomas and Steven Reid returned to the starting XI as Simon Cox and Gabriel Tamas made way. New signings Keith Andrews and Liam Ridgewell were among the subs, alongside Billy Jones and Paul Scharner, who both returned from injury. Shane Long (chest) missed his second successive game.
Brendan Rodgers named an unchanged team from the Swans' 1-1 draw with Chelsea while ex-Baggie Luke Moore was on the bench.
Albion started well but it was the visitors who threatened first. From a Leon Britton corner, the Baggies had to make two vital blocks to prevent Sigurdsson and Angel Rangel troubling Ben Foster's goal. The hosts only half-cleared another flag-kick but Joe Allen sent a weak effort wide from the edge of the box.
It didn't take long for the visitors to settle into their renowned passing stride and when they didn't have the ball, they got back in numbers and made it difficult for Albion to play through them.
On 17, Swansea won a free-kick in a dangerous position and Sigurdsson curled a fine effort, which Foster appeared to have covered, just wide.
Just a minute later, there was real controversy at the other end. Nick Shorey's corner came straight back to him and from his second centre, Gareth McAuley shaped to head goalwards but was denied by Ashley Williams' flailing arm. TV replays confirmed the Swansea skipper had handled - but referee Jonathan Moss waved away Albion's protests.
As the snow continued to fall gradually at The Hawthorns, James Morrison advanced onto Reid's ball and directed a fierce shot straight at Michel Vorm from 25 yards.
There was a big lull in proceedings until the 29th minute when Graham and McAuley contested Britton's lofted diagonal ball into the Baggies box. The Swansea striker reacted first to the rebound and fired just over from a tight angle.
The wintry weather was not conducive to flowing football and both teams struggled to get to grips with the conditions.
Albion didn't threaten again until the 38th minute when Mulumbu shot well wide from 25 yards after a brief spell of Baggies pressure.
At the other end, Allen saw a long-range effort clip McAuley and creep wide of the left-hand post.
But Albion really did go close in the 42nd minute as they piled on the pressure towards the end of the half. From Graham Dorrans' corner, Neil Taylor had to take evasive action at the near post to keep out Jonas Olsson's goalbound header.
Then, from Dorrans' second corner, Fortune saw a header cleared off the line by Sigurdsson. Odemwingie fired the rebound goalwards but this time Taylor got in the way.
On 44, Dorrans' angled free-kick into the box found Olsson whose goalbound half-volley from 12 yards was snaffled up by the well-positioned Vorm.
There was one last moment of note when Scott Sinclair went to ground in the box as he shaped to shoot, but referee Moss waved away Swansea's penalty claims. It looked as if the former Chelsea man had merely performed an air shot.
After the break, Swansea recorded the first shot, although it was a tame one, with Foster easily gathering Sigurdsson's deflected 25-yarder.
Some sloppy play by Mulumbu then gave Nathan Dyer a run at goal but he was off target from outside the box.
At the other end, Albion continued to look dangerous from set pieces - and they duly snatched a 54th-minute lead from one.
Olsson flicked Dorrans' corner to the back post and Fortune took one touch before firing into the far corner from a tight angle.
However, Albion's lead lasted just one minute. Swansea sprang forward down the left and from Taylor's pull-back, the unmarked Sigurdsson side-footed home from ten yards.
And the game was completely turned on its head on 59.
Sigurdsson whipped a terrific ball into the Baggies box from the right and Graham got in front of his marker to stab past a helpless Foster.
Albion attempted to regroup but surrendering their lead into a losing position had really sucked the wind out of their sails.
In fact, they were indebted to a wonderful last-ditch tackle by Olsson to keep out Dyer from Graham's pull-back.
Opportunity came and went for the Baggies on 71. Dorrans' cross-cum-shot found the unmarked Odemwingie at the far post - only for the Nigeria ace to blaze over an open net from seven yards.
Fortune was the next to try his luck, with his looping 25-yarder dipping just over.
Sub Scharner was far more accurate with Albion's next effort, but his 20-yard shot flew straight at Vorm.
On 85, Foster rushed off his line to prevent Dyer getting on the end of Rangel's slide-rule pass and Olsson blocked Sigurdsson's follow-up.
Back came Albion but sub Cox could only shoot straight at Vorm from 20 yards.
There was real Albion agony in the second minute of stoppage time when Fortune's 15-yard drive hit Vorm and squirmed inches wide.
The Swansea goal continued to live a charmed life during the dying seconds as the Baggies bombarded the Swansea box - but an equaliser eluded them.
ALBION (4-4-2): Foster; Reid, McAuley, Olsson, Shorey; Thomas (Tchoyi 71), Morrison, Mulumbu (Scharner 64), Dorrans (Cox 71); Odemwingie, Fortune. Subs not used: Fulop (gk), Andrews, Ridgewell, Jones.
SWANSEA (4-2-3-1): Vorm; Rangel, Caulker, Williams, Taylor; Sigurdsson, Allen; Sinclair, Britton, Dyer (Routledge 88); Graham. Subs not used: Tremmel (gk), Monk, McEachran, Lita, Moore, Agustien.
GOALS: ALBION - Fortune (54). SWANSEA - Sigurdsson (55), Graham (59).
BOOKINGS: ALBION - Morrison (foul 79), Shorey (dissent 90). SWANSEA - Britton (foul 43).
REFEREE: J Moss (West Yorkshire).
ATTENDANCE: 24, 274.
ALBION STARMAN: Marc-Antoine Fortune.