Report: Swans 1 West Brom 2
The Swans suffered a second consecutive home defeat as West Brom came from behind to win at the Liberty.
Graham Potter's side, beaten 4-1 by Norwich four days earlier, had led in the 10th minute thanks to Oli McBurnie's eighth goal of the campaign.
But two goals - both from corners - sank the Swans.
Just three minutes after taking the lead, the hosts were pegged back as Matt Phillips' deep corner was met by Craig Dawson, and his header looped over Erwin Mulder and into the net.
Then, a minute before the break, the Baggies were in front as Ahmed Hegazi headed in another deep corner at the back post.
Defeat leaves the Swans on 26 points from 19 games with a trip to Derby up next.
The Swans made two changes to the starting XI following the Norwich loss.
Centre-back Cameron Carter-Vickers took the place of Kyle Naughton as the American – on loan from Tottenham Hotspur – made his fifth appearance for the Swans.
The other change from the defeat to Norwich last weekend saw Graham Potter recall Martin Olsson, which meant Matt Grimes moved into midfield alongside skipper Leroy Fer and Bersant Celina.
Jay Fulton dropped to the bench, where Jefferson Montero was also included along with Wilfried Bony, who banked 45 minutes of game-time against Norwich City last weekend.
The Swans started brightly with the lively Daniel James latching onto Olsson's through ball before cutting inside and shooting low at Sam Johnstone.
They built on that by taking the lead as McBurnie teed up Grimes, whose shot was parried back to the Scottish striker, and he fired home from 15 yards.
The celebrations had barely died down by the time the visitors were level as Dawson headed home.
The Swans responded positively as James saw his shot deflected over for a corner while the winger then latched onto Celina's superb through ball but could only strike a tame effort at Johnstone.
But that good work was undone as Hegazi rose to nod home another corner just before the break.
The second half failed to match the opening 45 minutes in terms of goals or drama.
The Swans felt they should have been awarded a penalty when Dawson leaned into Olsson's cross, but referee James Linington was uninterested.
Fer flashed a volley over from a Celina corner before Baggies' Harvey Barnes struck the post at the other end.
Potter threw on Barrie McKay, Montero and Bony as they went in search of an equaliser, but it never came.
Another defeat at home means the Swans drop to 11th in the Championship.
Swans: Erwin Mulder, Connor Roberts (Barrie McKay, 61), Joe Rodon, Mike van der Hoorn, Cameron Carter-Vickers, Martin Olsson, Leroy Fer (capt, Jefferson Montero, 71), Matt Grimes, Bersant Celina, Daniel James (Wilfried Bony, 77), Oli McBurnie.
Subs: Kristoffer Nordfeldt, Kyle Naughton, Declan John, Jay Fulton.
West Brom: Sam Johnstone, Tosin Adarabioyo, Craig Dawson, Ahmed Hegazi, Kieran Gibbs, Matt Phillips, Jake Livermore (capt), James Morrison, Harvey Barnes (Dwight Gayle, 86), Hal Robson-Kanu (Gareth Barry, 90), Jay Rodriguez.
Subs: Boaz Myhill, Chris Brunt, Tyrone Mears, Wes Hoolahan, Rakeem Harper.
