ALBION suffered a miserable afternoon in South Wales as Swansea recorded their first-ever Barclays Premier League victory.
The Baggies started sluggishly and fell behind in the 14th minute when Scott Sinclair scored from the penalty spot after Paul Scharner had hauled down Joe Allen.
It was 2-0 ten minutes later when Leroy Lita headed home from close range and Swansea made the points safe four minutes after the break through Nathan Dyer.
The Baggies looked strangely subdued throughout and although they did improve in the second half, they will want to get this performance out of their system as soon as possible.
Craig Dawson was handed his Barclays Premier League debut in place of the suspended Gabriel Tamas while Roy Hodgson also recalled James Morrison, with Graham Dorrans dropping to the bench.
Chris Brunt was named among the subs after shaking off a knee problem.
Swansea made two changes from their narrow defeat at Arsenal as captain Garry Monk and Lita came in for injured duo Steven Caulker and Danny Graham.
Former Baggie Luke Moore was among the hosts' subs while another ex-Albion man, Craig Beattie, was ruled out by injury.
Before the game, a minute's silence was observed in memory of the four miners - Charles Breslin, 62, David Powell, 50, Garry Jenkins, 39, and Phillip Hill, 45 - who lost their lives in the mining tragedy at the nearby Gleision Colliery, Pontardawe.
Both teams also wore black armbands as a mark of respect. It was also an emotional occasion for Swans boss Brendan Rodgers on a personal level, as this was his first game in charge after the passing of his father, Malachy.
Swansea have become renowned for their possession-based brand of football and they certainly saw plenty of the ball during the opening stages, patiently prodding and probing for a way through the Albion defence.
Their first opening came in the seventh minute when Youssouf Mulumbu and Scharner got in a mix-up as they attempted to deal with Neil Taylor's weak cross.
The ball fell kindly for Sinclair but the ex-Chelsea man scuffed wide from an acute angle.
Two minutes later, Joe Allen drove at Steven Reid before seeing his low 15-yard drive gathered by Ben Foster at the second attempt.
Albion couldn't get out of their own half and the Swans' pressure told in the 13th minute when Scharner lunged in on Allen and conceded a penalty.
Sinclair made no mistake, sending Foster the wrong way to score City's first-ever Premier League goal.
The Baggies slowly regrouped and Taylor presented Shane Long with a great chance on 22 when he misplaced a cross-field pass straight to the Ireland international.
Unfortunately, Long failed to make the most of the gift, firing well over from just inside the box.
But Albion's afternoon went further downhill in the 24th minute.
Sinclair was left completely unmarked in the box to head Mark Gower's corner goalwards and Lita, also left unattended, headed home from three yards.
Albion had been woefully below par but almost pulled one back in the 32nd minute.
From Jerome Thomas' infield pass, Long unleashed a ferocious 25-yard effort which Michel Vorm brilliantly tipped over the bar at full stretch.
Albion won a corner six minutes later and from Morrison's delivery, Dawson headed straight at Vorm from 15 yards.
But Swansea continued to look comfortable and Nicky Shorey had to make a vital block a minute before the break to prevent Allen's shot from just inside the box troubling Foster after Sinclair had skipped down the left and centred.
Hodgson took action at half-time, replacing Thomas and Mulumbu with Brunt and Dorrans.
Brunt almost made an immediate impact when, from his corner, skipper Jonas Olsson saw his downward header cleared from inside the Swans' six-yard box by Monk.
But it appeared to be game over in the 49th minute - when Swansea made it 3-0 with a real route one effort. Lita flicked on Vorm's huge clearance and Dyer raced through before smashing the ball past Foster from ten yards.
Two minutes later, some neat build-up play created a shooting chance for Morrison on the edge of the City box, only for the Scotland international to drag his shot weakly wide of the left-hand post.
Albion were struggling to get any change out of the Swansea defence and Peter Odemwingie resorted to a long-range shot in the 56th minute, which sailed over.
Swansea were still playing neat stuff and, in the 59th minute, they won a free-kick in a dangerous position, which Sinclair curled over Foster's bar.
The Baggies had the ball in the net on the hour-mark when Brunt headed home Olsson's diagonal ball, but the effort was rightly ruled out for offside.
Albion had begun to peg the Swans back and won a free-kick of their own in the 64th minute.
Dorrans was mightily unlucky not to reverse the arrears, seeing his terrific right-foot curler superbly pushed away by Vorm at full stretch.
Dorrans also wasn't too far wide with a 25-yard missile before Odemwingie skipped past Taylor and saw his ferocious effort from an acute angle pushed wide by Vorm.
There was a lengthy delay during the closing stages when Taylor needed extended treatment after an accidental aerial clash with Odemwingie.
The Swansea defender worryingly left the field on a stretcher.
In stoppage time, Vorm had to be at his best to push away Long's downward header from Morrison's centre.
SWANSEA (4-3-3): Vorm; Rangel, Monk (C), Williams, Taylor (Bessone 85); Gower, Allen, Britton; Dyer (Routledge 70), Lita (Moore 70), Sinclair. Subs not used: Tremmel (gk), Dobbie, Richards, Lucas.
ALBION (4-4-2): Foster; Reid, Dawson, Olsson (C), Shorey; Morrison, Mulumbu (Brunt HT), Scharner (Cox 67), Thomas (Dorrans HT); Long, Odemwingie. Subs not used: Fulop (gk), Fortune, Jones, McAuley.
GOALS: SWANSEA - Sinclair (pen 14), Lita (24), Dyer (49).
BOOKINGS: SWANSEA - Lita (removing shirt 24). ALBION - Brunt (foul 58), Odemwingie (foul 79).
REFEREE: M Atkinson (West Yorkshire).
ALBION STARMAN: James Morrison.