In-form West Brom accepted Hull's gifts to pile more misery on the Tigers.
Chris Brunt and Gareth McAuley cashed in on errors before James Morrison clinched a 3-1 win for the Baggies at The Hawthorns.
Robert Snodgrass had given Hull a first-half lead, but the Tigers beat themselves during a second half littered with costly defensive mistakes.
"62 | McAuley heads in at the back post from a @WBA corner Clucas tried to clear off the line but GDS gives @WBA the goal #WBAHUL" - Hull's official account describes the second goal, awarded with the use of goal-line technology.
MOMENT OF THE MATCH:
Hull had been on top during the first half and needed to keep it tight after the break but shot themselves in the foot just four minutes into the second half.
Matt Phillips corner found Chris Brunt completely unmarked at the far post and the Northern Ireland international thumped a header past David Marshall.
It changed the game and Hull saw victory disappear with their non-existent defending as Gareth McAuley and James Morrison added to their woes.
VIEW FROM THE BENCH
Hull boss Mike Phelan would have been quietly confident coming out for the second half but his side unravelled.
They were calm and composed in the first half and comfortably on top but failing to mark Chris Brunt for Albion's equaliser changed the game.
Tony Pulis' words of wisdom at the break aided the Baggies' cause but he would have been far from happy with the way they started the game.
STAR MAN: Matt Phillips
The winger had a slow start to his West Brom career but has improved as the season has gone on to become an integral part of Tony Pulis' side.
He grabbed another two assists from corners - although was given a helping hand by poor Hull defending - having scored in Saturday's 2-1 win at Southampton.
Phillips was a long-term target for Pulis and has slowly shown why the manager persisted in his chase to sign him from QPR in the summer.
Ben Foster: 7 (out of 10)
Craig Dawson: 7
Gareth McAuley: 7
Jonny Evans: 7
Chris Brunt: 7
Darren Fletcher: 7
Claudio Yacob: 7
Nacer Chadli: 7
James Morrison: 7
Matt Phillips: 7
Salomon Rondon: 7
Allan Nyom (for Evans): 6
Hal Robson-Kanu (for Chadli): 6
James McClean (for Rondon): 6
David Marshall: 6
Harry Maguire: 6
Curtis Davies: 6
Michael Dawson: 7
Ahmed Elmohamady: 6
Tom Huddlestone: 6
Jake Livermore: 6
Robert Snodgrass: 7
Sam Clucas: 6
Dieumerci Mbokani: 6
Adama Diomande: 6
Ryan Mason (for Mbokani): 6
Markus Henriksen (for Davies): 6
WHO'S UP NEXT?
West Brom v Derby (Saturday, January 7, FA Cup)
Hull v Swansea (Saturday, January 7, FA Cup)