SHANE Long and Peter Odemwingie both bagged their fourth league goals of the season to stun the European champions and earn the buoyant Baggies a third successive win.
Long headed Albion in front in the tenth minute, only for Eden Hazard - with the aid of a Billy Jones deflection - to restore parity six minutes before the break.
But the hosts, who produced a performance of real maturity, weren’t to be denied and Odemwingie nodded home what proved the winner in the 50th minute – with Long this time the provider.
A sixth win in seven home games – and a proud one for Steve Clarke against his former employers – was lapped up by a packed Hawthorns crowd.
And the huge contribution of keeper Boaz Myhill, who produced three first-class saves, was not lost on them as Albion ended Chelsea’s unbeaten away record.
Fifth entertained third at The Hawthorns, with the two teams, who began the season with entirely different aspirations, separated by just four points.
The Baggies’ former promotion-winning gaffer, Roberto Di Matteo, was granted a warm welcome by the home fans as he embraced the current Hawthorns incumbent, and his former Chelsea colleague, Clarke just before kick-off.
Clarke rang three changes from the Wigan win, with Gabriel Tamas drafted in at centre-half in place of Gareth McAuley (leg) while Odemwingie and Zoltan Gera came in for the ineligible Romelu Lukaku and benched Chris Brunt. Steven Reid returned to the bench following more than two months out with a hamstring injury.
Chelsea enjoyed plenty of possession during the opening exchanges as Albion worked tirelessly to give the men in black as little time on the ball as possible.
In the seventh minute, Victor Moses got free down the left and his pull-back was somewhat mis-kicked goalwards by Ryan Bertrand. Thankfully for Albion, Liam Ridgewell was on hand to clear off the line. Hazard was first to the loose ball but his goalbound effort was blocked by skipper-for-the-day Jonas Olsson.
However, Albion began to gain a foothold in the game – and snatched a tenth-minute lead. James Morrison found space in the box and picked out Long at the back stick with a perfect centre. The former Reading man held off David Luiz to plant a diving header past Petr Cech from six yards. Cue delirium inside The Hawthorns!
The visitors regrouped and began prodding and probing for an equaliser. John Obi Mikel was only inches wide with a 30-yard grass-cutter. Then, on 17, Moses was well off target from similar distance.
There hadn’t been too many goalmouth incidents as the game ticked past the half-hour mark, but this was still turning into a fascinating contest.
Myhill had his first save to make on 32, which proved a simple one, as Daniel Sturridge drove a 20-yard half-volley straight at the Albion No.13.
A minute later, Long was incensed after the officials failed to award him a penalty as he bundled the ball at Cech from Jones’ cross, claiming Gary Cahill had impeded him.
Long was proving a real handful for the Chelsea defence and he went close again on 35 when he held off Cesar Azpilicueta and strode past Cahill before curling inches wide from 20 yards.
However, Chelsea restored parity six minutes before the break. Hazard spread the play before racing into the Baggies box to head Azpilicueta’s cross into the danger-zone. There would have been an easy catch for Myhill had the ball not clipped the luckless Jones’ head and been diverted into the net.
Chelsea now attacked with renewed purpose and Sturridge flashed a fierce shot just wide from 25 yards. Just before the half-time whistle, Luiz smashed a free-kick into the Albion wall, which looped wide of the left-hand post.
The West Londoners started the second 45 on the front foot and Myhill was forced to make a terrific block within two minutes of the re-start to keep out Sturridge’s snapshot from Moses’ centre.
That save proved pivotal – because Albion were back in front on 50. Morrison spearheaded a Baggies attack before finding Long on the right and his inch-perfect cross was glanced home by Odemwingie at the near post.
Back came Chelsea and only Olsson’s outstretched left leg, which somehow hooked away Azpilicueta’s low centre, denied Sturridge a tap-in.
Myhill was then afforded the adulation of the Smethwick End’s home section when he saved bravely at Moses’ feet - getting a kick in the ribs for his troubles - to prevent the ex-Wigan ace hooking home Hazard’s corner.
But Albion were giving as good as they were getting, although Gera would’ve been disappointed with a 20-yard free-kick, which he directed straight at Cahill in the Blues’ wall.
After Moses had had loud penalty appeals turned away following a clash in the box with the impressive Claudio Yacob, Myhill pulled off the save of the game when he somehow diverted wide Sturridge’s goalbound prod at point-blank range from sub Juan Mata’s chipped through-pass.
This was proving to be a Hawthorns cracker and Yacob well and truly stung Cech’s hands with a 30-yard pile-driver.
Myhill’s contribution kept getting bigger and on 78 he denied Sturridge in a one-on-one with a brilliant save low to his right after the Chelsea striker had raced onto Mata’s through-pass.
Myhill also showed a safe pair of hands to clutch Hazard’s deflected 15-yard shot on 85.
Chelsea were piling on the pressure and there was further agony for Sturridge when he shot inches wide from an acute angle from Oscar’s lay-off.
But the Baggies defended resolutely during the dying stages to secure their first back-to-back wins over Chelsea for 33 years.
ALBION (4-2-3-1): Myhill; Jones, Tamas, Olsson, Ridgewell; Yacob, Mulumbu; Odemwingie, Morrison (Dorrans 69), Gera (Brunt 69); Long (Rosenberg 80). Subs not used: L Daniels (gk), Popov, Reid, Fortune.
CHELSEA (4-2-3-1): Cech; Azpilicueta, Cahill, Luiz, Bertrand; Mikel (Ramires 81), Romeu (Oscar 62); Sturridge, Hazard, Moses; Torres (Mata 62). Subs not used: Turnbull (gk), Ivanovic, Cole, Marin.
GOALS: ALBION – Long (10), Odemwingie (50). CHELSEA – (Jones own goal, 39).
REFEREE: M Oliver (Northumberland).
ALBION STARMAN: Boaz Myhill.