Chelsea cruised to a comfortable win to move joint top of the Premiership and pile pressure on beleaguered Albion.
Following the departure of manager Gary Megson, the hosts battled hard before a William Gallas goal on the stroke of half-time opened the floodgates.
The Frenchman hammered home from close range and soon after the re-start it was two when Eidur Gudjohnsen scored.
While Zoltan Gera's driven shot gave Albion hope, goals from Damien Duff and Frank Lampard ended the rout.
Stand-in Albion manager Frank Burrows, in his trademark cloth cap, cut a contrasting figure to slick-suited visiting boss Jose Mourinho.
And those differing styles were expected to be mirrored on the pitch, with Albion's more agricultural style proving little resistance to the Kings Road artists.
That is how it transpired, but Albion started with a spirit that belied Megson's criticism of his squad's attitude.
Kanu's cameos were more than just window dressing and the languid Nigerian went close on two occasions in the early exchanges.
While he pulled the strings in attack, with the impressive Gera a constant menace, Darren Moore marshalled the defence to good effect.
However, their efforts all too often foundered with Robert Earnshaw, who, while full of endeavour, looked out of his depth against the Premiership's most parsimonious defence
Chelsea were crisp and composed in their build-up, but lacked a cutting edge in the penalty area and Gudjohnsen looked isolated up front.
However, with the job nearly half done from a home perspective and the sanctuary of the dressing room beckoning, Albion let their concentration slip.
John Terry lost Moore and stooped to head a Lampard corner into the path of Gallas, his fellow defender firing beyond a helpless Russell Hoult from close range.
Mourinho's half-time changes - Ricardo Carvalho for Wayne Bridge and Arjen Robben for Joe Cole - helped spark further life into the game with three goals in the first 15 minutes of the second period.
Hoult was again exposed when Gudjohnsen bisected the defence to rise unchallenged and head in Duff's cross from the left.
Gera halved the deficit when he lashed in a low, fizzing shot from the edge of the area after Kanu's initial effort was blocked, but Chelsea soon re-opened their two-goal advantage.
In the blink of an eye they broke from defence to attack and Lampard's raking pass found Duff on the right, the Irishman neatly clipping the ball over Hoult.
Chelsea looked happy to play out time, but with the clock ticking down the excellent Robben played in Lampard who fired in from outside the area to make it eight goals in two games for the previously goal-shy Blues.
With Adrian Mutu sacked and Didier Drogba on the treatment table Chelsea are supposed to have a threadbare attack.
How Albion fans must crave such a crisis after losing a manager and their unbeaten home record in the space of a week.
West Brom: Hoult, Scimeca, Gaardsoe, Moore, Robinson, Gera,
Johnson, Clement (Koumas 64), Greening (Dyer 80),
Earnshaw (Dobie 56), Kanu.
Subs Not Used: Haas, Kuszczak.
Goals: Gera 56.
Chelsea: Cech, Paulo Ferreira, Terry, Gallas,
Bridge (Ricardo Carvalho 46), Smertin, Makelele,
Lampard (Tiago 83), Cole (Robben 46), Gudjohnsen, Duff.
Subs Not Used: Kezman, Cudicini.
Goals: Gallas 45, Gudjohnsen 51, Duff 59, Lampard 81.
Ref: B Knight (Kent).