ALBION proved the architects of their own downfall as they were hit for six by champions Chelsea on the opening day of the season.
Basic errors at either end of the first half cost the visitors dearly - and hat-trick hero Didier Drogba was in an unforgiving mood.
Scott Carson's early spill allowed Florent Malouda, who also grabbed the last goal in the final minute, to open the scoring in the sixth minute.
And the Baggies' wall parted like the Red Sea for Drogba to fire home the first of his treble seconds before the half-time whistle.
Another for the Ivory Coast hitman 12 minutes into the second half and his third in the 68th minute sandwiched a 63rd-minute Frank Lampard strike.
But it could, perhaps, have been a different story had Albion gone in just 1-0 down at the break as they showed enough going forward in the opening 45 minutes to keep the Blues defence on their toes.
Pablo Ibanez (hamstring) and Graham Dorrans (groin) both won their fitness race to make Roberto Di Matteo's opening-day starting XI.
The Baggies boss opted for a five-man midfield and started Roman Bednar - fresh from scoring his first international goal for the Czech Republic in midweek - as the lone striker.
Di Matteo received a hero's welcome from the home hordes as he walked out just before kick-off back on his old stomping ground.
But the hosts looked in no mood to do the Blues legend any favours as they started with a purpose.
However, despite all their possession, it was the visitors who threatened first in the third minute as Dorrans teed up James Morrison, who fired wide of the right-hand post from 18 yards.
A minute later, Carson was given a feel of the ball as he tucked himself in behind Nicolas Anelka's long-range effort.
But just as the Baggies looked to be bedding into the game, Carson spilt a routine take from Drogba's central free-kick.
The Albion skipper blocked John Obi Mikel's follow-up but was helpless to stop Malouda tapping home past Chris Brunt on the goalline for a sixth-minute opener.
Dorrans tried his luck from distance in the 11th minute and his shot deflected off Michael Essien to force Petr Cech into a low save to his right.
Dorrans slid Bednar through on goal eight minutes later and he finished well past fellow countryman Cech - but the whistle had already gone for offside against the former Hearts hitman.
Albion started to look at home in their top-flight surroundings and began to stroke the ball around with confidence.
Jerome Thomas looked a constant threat down the left and it wasn't until six minutes before the break that Chelsea threatened again.
Lampard's flick inside gave Malouda a sight of goal, but just as he was about to pull the trigger from 15 yards, Gonzalo Jara made a vital last-ditch clearance.
A minute later, Carson made amends for his earlier error with a flying block from Lampard's fizzing free-kick and Malouda nodded the rebound over.
At the other end, Chris Brunt was unfortunate to see his goalbound 18-yard strike blocked by John Terry.
But Albion gifted the champions another goal in the first minute of stoppage time.
Brunt and Gabriel Tamas parted in the Baggies wall, giving Carson no chance as Drogba's free-kick strike flew into the bottom right-hand corner of the net to double the lead.
The Baggies regrouped during the interval and Thomas' pass gave Dorrans a sight of goal seven minutes into the second half.
The Scot's 25-yard effort clipped off Bednar's heels and flew just a yard past the right-hand post, with Cech stranded.
Two minutes later, Dorrans curled a 25-yard free-kick agonisingly onto the roof of the net.
Back came the champions and a second Malouda corner in quick succession saw the unmarked Terry's near-post header cleared off the line by Youssouf Mulumbu.
But the former PSG midfielder then got in a mix-up with Brunt and the ball rolled to Drogba, who smashed home from ten yards to make it 3-0 in the 57th minute.
Six minutes later, neat football between Anelka and Ashley Cole saw the latter present Lampard with the simplest of chances that he comfortably despatched to make it four.
Di Matteo made a double change in the 67th minute as Ishmael Miller and Simon Cox came on for Bednar and Dorrans respectively.
Not even luck was on Albion's side as Drogba's hopeful long-range effort clipped off Tamas' head and flew past the helpless Carson to give the Ivory Coast striker his hat-trick in the 68th minute.
Albion came close to at least getting on the scoresheet four minutes from time when a swift counter-attack resulted in Marek Cech cutting the ball back for Brunt, whose goalbound strike was headed just over by Alex, with Cech stranded.
The Baggies came close again two minutes later when substitute Cox stepped inside Mikel and drilled a low shot just past the left-hand upright.
However, it was Carlo Ancelotti's men who wrapped up the scoring when Malouda eased onto Anelka's pass before rounding Carson and firing in off the near post to make it six.
CHELSEA (4-1-2-3): P Cech; Ferreira (Ivanovic 60), Alex,Terry, Cole; Mikel; Essien, Lampard (Benayoun 64); Anelka, Drogba (Kalou 70), Malouda. Subs not used: Hilario (gk), Zhirkov, Sturridge, Van Aanholt.
ALBION (4-2-3-1): Carson; Jara, Ibanez, Tamas, M Cech; Mulumbu, Brunt; Morrison, Dorrans (Cox 67), Thomas (Barnes 84); Bednar (Miller 67). Subs not used: Myhill (gk), Shorey, Olsson, S Reid.
GOALS: CHELSEA - Malouda (6, 90), Drogba (45+1, 57 &amp; 68), Lampard (63).
BOOKINGS: CHELSEA - Ferreira (foul 57).
REFEREE: M Clattenburg (Tyne &amp; Wear).
ALBION STARMAN: Jerome Thomas.