Stoke gave their play-off hopes a major boost as they dented shambolic West Brom's chances of automatic promotion from the Coca-Cola Championship.
Baggies manager Tony Mowbray had called for wins against the Potters and Norwich on Monday to stay in touch with the top two.
But having gifted City three goals in the space of eight first-half minutes, those ambitions looked more than fanciful.
The outstanding Ricardo Fuller's 10th of the season came after 13 minutes following and error by Sam Sodje and the Jamaican's cross then caused Jonathan Greening to turn the ball into his own goal.
Fuller then laid on a third for Jon Parkin in the 22nd minute to all but end the contest.
The second half was a non-event despite Jason Koumas pulling one back in his 100th league appearance for the Baggies, who have now won one in eight and have not recorded a victory in five matches at the Hawthorns.
The hosts were nervy from the first whistle, with Stoke enjoying a good early spell that saw John Eustace drive narrwly wide from the edge of the box.
Koumas was soon prompting the Baggies and six yards out, Kevin Phillips should have done better with the Welshman's cross.
Greening, Phillips and Koumas each fired narrowly off target for the home team but in the 14th minute, the Potters took the lead.
West Brom defender Sodje's inexplicable back-header seemed to have been dealt with by Paul Robinson, but in one motion, Fuller nicked the ball and dispatched it into the corner with his next.
Frustration immediately set in at the Hawthorns and soon they were two behind.
With 19 minutes gone, Fuller beat Sodje to the ball on the left flank and cut in towards goal before hitting a low cross that was diverted into his own goal by Greening.
Two minutes later the deficit was widened again, with Fuller latching onto Greening's wayward pass, showing blistering pace to get behind the West Brom defence, and then having the vision to lay it back for Parkin, who swept the ball home.
Richard Chaplow and Robert Koren each fired over from outside the area, while Nathan Ellington's dipping strike was only denied by the crossbar in the 36th minute.
Parkin could have made it four but headed over from close-range before Koumas finally forced a save from Potters goalkeeper Steve Simonsen in added time.
Greening, Sodje and Phillips were all replaced at the break but with Diomansy Kamara and Zoltan Gera left on the bench, Mowbray's intentions were unclear.
Koren and Ellington shot wide shortly after the restart, before substitute Darren Carter skimmed the post in the 53rd minute.
Another half-time replacement Jared Hodgkiss had an effort chalked off for offside after 55 minutes as Stoke were happy to sit back.
After further hopeful strikes from Koren and Koumas, Fuller's flick was met by a half-volley from Liam Lawrence in a rare Stoke attack.
With 16 minutes left, Koumas' deflected effort from just outside the area narrowed the deficit.
Carter had a free-kick saved by Simonsen shortly after but the Baggies never looked like getting a second.
Teams:
West Brom Kiely, Albrechtsen, McShane, Sodje (Hodgkiss 46),Robinson, Koren, Greening (Carter 46), Chaplow, Koumas,Phillips (MacDonald 46), Ellington.
Subs Not Used: Gera, Kamara.
Booked: Phillips, Carter.
Goals: Koumas 74.
Stoke Simonsen, Hoefkens, Fortune, Zakuani, Higginbotham,Lawrence, Eustace, Matteo, Dickinson, Sidibe (Parkin 17),Fuller (Martin 90), Parkin (Hendrie 65).
Subs Not Used: Hoult, Vass.
Booked: Higginbotham, Fuller, Hendrie.
Goals: Fuller 14, Greening 21 og, Parkin 22.
Att: 20,386
Ref: P Taylor (Hertfordshire).