ALBION were denied their first win at Stamford Bridge in more than 35 years by a controversial last-gasp penalty.
Second-half goals from Shane Long and Stephane Sessegnon cancelled out Samuel Eto’o’s opener on the stroke of half-time.
The Baggies looked to be heading for a famous and deserved victory when, in the fifth minute of stoppage time, referee Andre Marriner controversially awarded the hosts a penalty after Steven Reid clashed with Ramires inside the box.
TV replays suggested the decision was harsh to say the least.
But, after vociferous protests fell on deaf ears, Albion’s players could only look on aghast as Eden Hazard converted the spot-kick to save Jose Mourinho from his first-ever home league defeat as Chelsea boss.
Steve Clarke made two changes to his starting XI – one enforced. Reid came in for the injured Billy Jones (hamstring) at right-back and Claudio Yacob replaced the benched James Morrison in midfield.
The Albion chief’s former boss Mourinho made four changes with Gary Cahill, Cesar Azpilicueta, Willian and Eto’o coming in for benched trio David Luiz, Ashley Cole and Juan Mata, and the injured Fernando Torres.
The first effort of the game came from the Baggies in the eighth minute when Long managed to knock Jonas Olsson’s long punt down for Morgan Amalfitano. The France international chose to shoot from 25 yards instead of pick out a team-mate and dragged the ball wide of the left-hand post.
Three minutes later, Eto’o spun in the box and his strike deflected off Olsson and into the arms of birthday boy Boaz Myhill.
Youssouf Mulumbu needed treatment after Frank Lampard’s free-kick hit him where it hurts in the 15th minute – but he soon shook it off after a few grimaces.
Eto’o just could not stretch far enough to direct his header from Willian’s right-wing cross on target on 19.
At the other end, Gareth McAuley looked like nodding home Chris Brunt’s corner five minutes later but Branislav Ivanovic showed good strength to beat him to the ball.
Yacob was booked for fouling Eden Hazard 20 yards from goal approaching the half-hour mark and from the resultant free-kick, Oscar’s curler looked to be heading for the top right-hand corner of the net until Myhill’s intervention.
Moments later, the Wales international did well to punch clear Lampard’s free-kick among a crowd of players before Liam Ridgewell blocked Hazard’s goalbound shot from the rebound.
The game looked to be heading for deadlock at half-time but seconds before the break, Hazard drifted in past Amalfitano and Reid before letting off a low curling shot towards the far post.
Myhill did brilliantly to swoop and parry it away but Ridgewell dallied on the rebound in the six-yard box, allowing Eto’o to nip in and open the scoring.
The hosts came close to doubling their lead five minutes into the second half when Oscar hit a sublime diagonal ball into the box for Hazard, whose touch was too heavy and allowed Myhill to gather the ball.
Brunt delivered a superb corner to the back post on 53, which just evaded Gareth McAuley. Olsson did manage to connect but directed his header wide under pressure from Ivanovic.
The Baggies came within a whisker of equalising three minutes later when Long’s header from Amalfitano’s right-wing cross beat Petr Cech but clipped the outside of the far post.
McAuley beat Cech to Brunt’s free-kick on 58 but the ball looped over the bar to safety as the visitors’ pressure on the Chelsea goal grew.
McAuley looked certain to score from an Amalfitano corner on the hour-mark but he headed straight at Cech and the chance looked to have gone. However, the persistent Long leapt above Terry, Lampard and Ivanovic to nod home the rebound and level the scores.
Mourinho made his first change on 64 as Lampard made way for Demba Ba.
Yacob’s determination to win the ball from Ivanovic in his own half paid off as he sprung Ridgewell on the attack.
The left-back did well to combine with Sessegnon and atoned for his earlier mistake by squaring for the Benin international, who coolly left Terry on his backside before firing home a left-foot shot through Cech to give the buoyant Baggies a deserved lead.
Chelsea made a double switch on 73 as Mikel and Juan Mata came on for Azpilicueta and Oscar.
Myhill produced heroics on 77 as he pulled off a point-blank save from Ivanovic’s volley, with Cahill putting the rebound into the side-netting.
Ten minutes from time, Willian should have levelled from Hazard’s cross – but headed over.
The Baggies survived another late scare when Cahill’s centre flew inches behind Ba in the six-yard box.
Albion could – and probably should – have made it three in stoppage time when Brunt and substitute Victor Anichebe burst through two on one. The former chose to shoot but blazed over.
Moments later, Ramires bounced off Reid in the box and referee Marriner harshly pointed to the spot. Hazard stepped up to slot home the penalty, pinch a point and deny Albion in the cruelest of circumstances.
CHELSEA (4-2-3-1): Cech; Ivanovic, Cahill, Terry, Azpilicueta (Mikel 73); Ramires, Lampard (Ba 64); Hazard, Oscar (Mata 73), Willian; Eto'o. Subs not used: Schwarzer (gk), Cole, Luiz, De Bruyne.
ALBION (4-2-3-1): Myhill; Reid, McAuley, Olsson, Ridgewell; Yacob, Mulumbu; Amalfitano (Popov 88), Sessegnon (Morrison 81), Brunt; Long (Anichebe 79). Subs not used: L Daniels (gk), Dawson, Berahino, Vydra.
GOALS: CHELSEA – Eto’o (45), Hazard (pen 90+6). ALBION – Long (60), Sessegnon (68).
BOOKINGS: CHELSEA – Lampard (foul 15), Hazard (over-celebrating 45+1). ALBION – Yacob (foul 29), Long (foul 45+3), Amalfitano (foul 83), Brunt (dissent 90+5), , McAuley (dissent 90+5), Ridgewell (dissent 90+6), Olsson (dissent 90+7).
REFEREE: A Marriner (West Midlands).
ALBION STARMAN: Shane Long.