ALBION proved the architects of their own downfall as they suffered another disappointing day at the Liberty Stadium.
For the third time in four seasons, the Baggies shipped three goals on Swans soil as the hosts cruised to victory.
Alan Irvine’s men gave themselves an uphill battle by conceding to Nathan Dyer inside 90 seconds.
Wayne Routledge made it 2-0 with a superb 24th-minute strike.
And Dyer completed the scoring on 71 to make it three Barclays Premier League wins out of three for the South Wales outfit this term.
Brown Ideye and Jason Davidson were handed their full Premier League debuts as Irvine made two changes to his top-flight starting XI.
Garry Monk named an unchanged Swans team to the one that made it two wins in as many league games against Burnley last weekend.
The Baggies got off to the worst possible start as Gylfi Sigurdsson flicked the ball in behind their defence.
Jonas Olsson lost his footing allowing Dyer to nip in, round Ben Foster and slot home from a tight angle after just 87 seconds.
In the ninth minute, Wilfried Bony pounced on indecision between Youssouf Mulumbu and Craig Gardner to fire a fierce 30-yard drive just over.
Five minutes later, Bony headed Dyer’s right-wing cross over the bar.
Craig Dawson came to the rescue on 20 as he pipped Bony to Jonjo Shelvey’s attempted through-ball.
The Baggies were causing their own problems, with Chris Brunt miscuing his clearance straight to Shelvey. The former Liverpool midfielder’s cross led to Dawson heading the ball to the feet of Routledge, whose stunning first-time volley from the edge of the box flew just inside the right-hand post to double the Swans’ lead on 24.
Olsson was having no luck and the crossbar came to his rescue as he unwittingly headed Routledge’s cross back towards his own goal.
It was all City, and moments later Bony fed Sigurdsson in the box but he scuffed his left-footed shot and Foster was able to gather comfortably.
Albion’s first real effort of the game came five minutes before the break when Ideye showed good skill to beat Jordi Amat before seeing his low shot easily held by Lukasz Fabianski.
The visitors did not appear to be learning from their mistakes and on 45 Dawson’s clearance from Shelvey’s corner fell to the unmarked Routledge, who came within a whisker of grabbing his second of the game with a swerving 15-yard volley.
Irvine made a change at half-time, with Stephane Sessegnon coming on for Dorrans.
Albion started the second half brightly, with Craig Gardner drilling a 25-yard free-kick into the wall.
But the Swans were still threatening through Dyer, whose 50th-minute cross just evaded Bony in the middle.
Three minutes later, Routledge broke and when Dawson dispossessed him, Bony pounced on the loose ball to feed Routledge again.
This time the former Crystal Palace winger lofted a cross to the back post, where Foster just managed to beat Sigurdsson to the ball.
Saido Berahino earned a corner in the 56th minute, which Brunt delivered to the back post, only for Olsson to head wide.
Referee Paul Tierney controversially awarded Swansea a free-kick for a supposed back-pass by Dawson on 65.
The ball was rolled to Bony, who first effort was blocked on the line by Andre Wisdom and his second from the rebound saved by Foster.
A minute later, Monk made his first change as Jefferson Montero came on for Routledge.
The substitute almost made an immediate impact after he broke free down the left and centred for Bony, who should have made it three – but blazed over.
The hosts did add a third on 71 as Dyer raced clean through onto Sigurdsson’s pass and confidently slid the ball home low to Foster’s left.
That prompted a double change by Irvine, with Cristian Gamboa and James Morrison coming on for Davidson and Brunt respectively.
Sessegnon almost pulled one back for the Baggies on 76, only to see his 15-yard strike cannon back off the bar.
Seconds later, Gardner’s shot from just outside the box fizzed just wide of the left-hand post.
Berahino went close in the 79th minute when his shot was deflected inches wide off Ashley Williams.
Morrison let fly with a 25-yard effort on 83 and Fabianski had to dive high to his left to palm it away.
SWANSEA (4-2-3-1): Fabianski; Rangel, Amat, Williams (c), Taylor; Ki, Shelvey (Carroll 84); Dyer, Sigurdsson, Routledge (Montero 66); Bony (Gomis 76). Subs not used: Tremmel (gk), Tiendalli, Fernandez, Richards.
ALBION (4-2-3-1): Foster; Wisdom, Dawson, Olsson, Davidson (Gamboa 72); Gardner, Mulumbu; Berahino, Dorrans (Sessegnon HT), Brunt (c) (Morrison 72); Ideye. Subs not used: Myhill (gk), McAuley, Yacob, Baird.
GOALS: SWANSEA – Dyer (2, 71), Routledge (24).
BOOKINGS: ALBION – Dorrans (foul 27), Gardner (foul 62).
REFEREE: P Tierney (Lancashire).
ALBION STARMAN: Craig Gardner.