Gareth McAuley's late goal earned West Bromwich Albion a third straight league win to pile more pressure on Chelsea manager Andre Villas-Boas.
McAuley diverted in Liam Ridgewell's miscued shot to secure the points from an open match that raises further questions about Villas-Boas's future.
Daniel Sturridge missed two fine chances for Chelsea, who have only won three of their last 12 league games.
But the Baggies dominated the latter stages and were good value for the win.
Even the most ardent Blues fan would struggle to argue against a result which leaves them fifth in the table, three points behind an improving Arsenal side, and in serious danger of failing to qualify for the Champions League.
And the relentless pressure on the Portuguese will surely only increase if they fail to overturn a 3-1 first-leg deficit against Napoli in their Champions League last 16 tie on Wednesday, 14 March to progress in Europe.
Before they look to progress against the odds in Europe, Chelsea also face a tricky FA Cup fifth-round replay against Birmingham on Tuesday .
Owner Roman Abramovich has so far refused to publicy back the man he appointed at great expense in the summer and there was precious little Villas-Boas could point to from their display at the Hawthorns to convince Abramovich he deserves his unwavering support.
The Baggies were full of energy, won the midfield battle and denied Chelsea time and space to end a run of 11 straight Premier League defeats against the Blues.
Did you know?
This is the first time West Brom have registered three consecutive Premier League victories since August-September 2002
Chelsea will point to two glorious opportunities spurned by Sturridge either side of the break.
And although the hosts had the greater share of possession and territory throughout, the Blues had the better chances before half-time.
Sturridge, back in the side despite limping out of the midweek England friendly against Holland with a toe injury, missed the best one when he dragged his shot wide after running on to a brilliant pass from Didier Drogba.
Gary Cahill also had a fierce 12-yard strike blocked by the on-rushing James Morrison, and the lively Juan Mata tested keeper Ben Foster from close range after great build-up play involving Michael Essien and Drogba.
But it was Sturridge's second opportunity after the interval that will play heavily on his mind. The striker tried to let the ball run on as Foster came tearing out of his penalty area and the keeper read Sturridge's mind and was able to clear.
Lampard also went close with a low strike in injury-time.
However Albion bossed the final 30 minutes and Petr Cech, whose only notable first-half save came from Morrison's long-range effort, was forced into a number of good stops.
The Czech number one made a superb low block from Marc Antoine-Fortune and tipped over a fierce Youssouf Mulumbu strike.
And although many of Cech's other saves were fairly routine, the home side's pressure finally told against an increasingly ragged Chelsea side.
The Blues were desperately piling forward in search of a winner but the Baggies retained their organisation and composure and secured a deserved victory with eight minutes remaining.
Chelsea failed to clear a corner and McAuley turned the ball in from close range from Ridgewell's scuffed shot following a Keith Andrews cross.
Albion held on with relative ease to move 13 points clear of the relegation zone.
West Bromwich Albion
- 01 Foster
- 03 Olsson
- 06 Ridgewell Booked
- 23 McAuley
- 07 Morrison
- 08 Andrews Booked
- 12 Reid (Tamas - 57' )
- 14 Thomas (Brunt - 64' Booked )
- 21 Mulumbu
- 24 Odemwingie
- 32 Fortune (Long - 84' )
- 13 Fulop
- 20 Shorey
- 30 Tamas
- 11 Brunt
- 17 Dorrans
- 09 Long
- 31 Cox
- 01 Cech
- 02 Ivanovic (Meireles - 84' )
- 03 Cole Booked
- 04 Luiz
- 24 Cahill
- 05 Essien (Torres - 76' )
- 07 Ramires
- 08 Lampard
- 10 Mata
- 11 Drogba
- 23 Sturridge (Malouda - 63' )
- 22 Turnbull
- 27 Hutchinson
- 06 Romeu
- 12 Mikel
- 15 Malouda
- 16 Meireles
- 09 Torres
Live Text Commentary
Full Time The referee signals the end of the game.90:00 +3:44
Free kick crossed left-footed by Juan Mata from right channel, clearance by Youssouf Mulumbu.90:00 +3:44 Booking
Booking Chris Brunt booked.90:00 +3:29
Chris Brunt concedes a free kick for a foul on Ramires.90:00 +2:42
Effort from the edge of the box by Juan Mata goes wide of the left-hand post.90:00 +1:01
Ashley Cole crosses the ball, Effort from inside the area by Frank Lampard misses to the right of the goal.89:38
Juan Mata takes the outswinging corner, Close range header by Didier Drogba goes over the crossbar.89:02
Centre by Raul Meireles, Gareth McAuley manages to make a clearance.86:04
Florent Malouda challenges Youssouf Mulumbu unfairly and gives away a free kick. Chris Brunt produces a strike on goal direct from the free kick.85:39
Corner taken by Chris Brunt played to the near post, clearance made by Frank Lampard.85:26
Keith Andrews takes a shot. Petr Cech makes a save.84:44
Free kick crossed left-footed by Chris Brunt, Raul Meireles manages to make a clearance.84:44 Booking
Booking Ashley Cole is shown a yellow card for unsporting behaviour.84:39
Free kick awarded for an unfair challenge on Shane Long by Ashley Cole.83:22 Substitution
Substitution Branislav Ivanovic goes off and Raul Meireles comes on.83:22 Substitution
Substitution (West Brom) makes a substitution, with Shane Long coming on for Marc-Antoine Fortune.81:33
The assist for the goal came from Liam Ridgewell.81:33 Goal scored
Goal! - Gareth McAuley - West Brom 1 - 0 Chelsea A goal is scored by Gareth McAuley from inside the six-yard box to the bottom left corner of the goal. West Brom 1-0 Chelsea.80:15
The ball is crossed by Chris Brunt, clearance by Ashley Cole. Chris Brunt takes a inswinging corner from the right by-line played to the near post, clearance by Frank Lampard. Inswinging corner taken by Chris Brunt from the right by-line, Petr Cech makes a save.80:02
Centre by Peter Odemwingie, Ramires makes a clearance.
Free kick crossed by Juan Mata, clearance by Chris Brunt.78:50 Booking
Booking The referee shows Keith Andrews a yellow card.78:45
Fernando Torres fouled by Keith Andrews, the ref awards a free kick.77:29
The ball is sent over by Juan Mata, clearance by Gareth McAuley.75:31 Substitution
Substitution Fernando Torres joins the action as a substitute, replacing Michael Essien.75:18
Chris Brunt takes a shot from a long way out which goes wide of the right-hand upright.74:56
The ball is sent over by Branislav Ivanovic, Ben Foster makes a save.74:19
Branislav Ivanovic sends in a cross, clearance made by Jonas Olsson.73:15
Chris Brunt takes a shot. Save by Petr Cech.70:21
The ball is crossed by Liam Ridgewell, Ashley Cole makes a clearance. Chris Brunt takes a outswinging corner to the near post, Liam Ridgewell produces a header from inside the six-yard box that clears the bar.69:44
Michael Essien produces a cross, clearance by Gabriel Tamas.69:29
The ball is swung over by Branislav Ivanovic, Jonas Olsson manages to make a clearance.68:06
Marc-Antoine Fortune takes a shot. Save by Petr Cech.65:49
Marc-Antoine Fortune takes a shot. Ashley Cole gets a block in. Corner taken left-footed by Chris Brunt, Youssouf Mulumbu takes a shot. Save by Petr Cech. Inswinging corner taken left-footed by Chris Brunt from the right by-line, clearance made by Ashley Cole.65:20
Free kick taken by Juan Mata.65:20 Booking
Booking Liam Ridgewell goes into the referee's book for unsporting behaviour.64:46
Free kick awarded for an unfair challenge on Ramires by Liam Ridgewell.63:10 Substitution
Substitution Chris Brunt joins the action as a substitute, replacing Jerome Thomas.62:46 Substitution
Substitution (Chelsea) makes a substitution, with Florent Malouda coming on for Daniel Sturridge.61:36
Juan Mata produces a left-footed shot from just outside the box that misses to the right of the net.60:55
The assistant referee flags for offside against Marc-Antoine Fortune. Gary Cahill restarts play with the free kick.58:57
The ball is crossed by Peter Odemwingie, Frank Lampard manages to make a clearance. Corner taken right-footed by James Morrison, Foul by Peter Odemwingie on Petr Cech, free kick awarded. Petr Cech takes the direct free kick.58:16
Marc-Antoine Fortune takes a shot. Save by Petr Cech.58:12
The ball is crossed by Liam Ridgewell.56:11
Petr Cech takes the free kick.56:11 Substitution
Substitution Steven Reid leaves the field to be replaced by Gabriel Tamas.56:11
Michael Essien fouled by Marc-Antoine Fortune, the ref awards a free kick.52:16
Unfair challenge on Steven Reid by Didier Drogba results in a free kick. The free kick is swung in right-footed by James Morrison, clearance made by Branislav Ivanovic.51:21
Didier Drogba takes a shot. Gareth McAuley gets a block in.49:40
Liam Ridgewell challenges Daniel Sturridge unfairly and gives away a free kick. Branislav Ivanovic takes the direct free kick.46:55
Foul by Steven Reid on Ramires, free kick awarded. Juan Mata delivers the ball from the free kick left-footed from left wing, Jonas Olsson makes a clearance.45:01
The second half begins.45:00 +3:10 Half time
Half Time The ref blows to signal half-time.45:00 +2:52
Jerome Thomas sends in a cross, Branislav Ivanovic makes a clearance.45:00 +2:31
Outswinging corner taken right-footed by James Morrison from the right by-line.45:00 +2:02
Youssouf Mulumbu takes a shot. Blocked by Gary Cahill.45:00 +1:49
Jerome Thomas produces a cross, clearance made by Branislav Ivanovic.45:00 +1:05
The ball is crossed by Daniel Sturridge, save made by Ben Foster.45:00 +0:24
James Morrison crosses the ball, clearance by Gary Cahill.44:57
Corner taken short by Peter Odemwingie.43:46
Free kick awarded for a foul by Branislav Ivanovic on Marc-Antoine Fortune. Liam Ridgewell takes the direct free kick.42:10
Michael Essien concedes a free kick for a foul on James Morrison. Jonas Olsson takes the direct free kick.41:13
Outswinging corner taken from the right by-line by James Morrison, clearance by Didier Drogba.40:27
Foul by Ramires on Keith Andrews, free kick awarded. Direct free kick taken by Jonas Olsson.39:36
Daniel Sturridge has an effort at goal from the edge of the box that misses to the right of the target.39:00
Liam Ridgewell delivers the ball.38:13
Michael Essien takes a shot. Brilliant save by Ben Foster.38:01
Juan Mata delivers the ball, clearance made by Gareth McAuley.37:39
Inswinging corner taken left-footed by Juan Mata, Gareth McAuley makes a clearance.37:27
Daniel Sturridge takes a shot. Liam Ridgewell gets a block in.36:19
Liam Ridgewell produces a cross, clearance by Branislav Ivanovic. James Morrison takes the inswinging corner, Close range headed effort by Keith Andrews goes wide of the left-hand post.36:03
The ball is sent over by Steven Reid, Gary Cahill manages to make a clearance.34:49
The ball is sent over by Ashley Cole.34:17
A cross is delivered by Ramires, Gareth McAuley makes a clearance.31:03
Shot from just outside the box by Youssouf Mulumbu goes over the crossbar.30:55
The ball is delivered by James Morrison, Didier Drogba makes a clearance.30:17
The ball is delivered by Peter Odemwingie, David Luiz gets a block in. James Morrison takes a outswinging corner to the near post, clearance made by Gary Cahill.29:41
Free kick awarded for a foul by Gary Cahill on Marc-Antoine Fortune. James Morrison takes the direct free kick.28:18
Shot from long distance by Didier Drogba goes over the bar.27:49
Marc-Antoine Fortune gives away a free kick for an unfair challenge on Gary Cahill. Michael Essien takes the direct free kick.26:43
Gary Cahill takes a shot. Blocked by Liam Ridgewell.26:09
Corner taken by Frank Lampard from the left by-line to the near post, Steven Reid makes a clearance.25:02
Foul by Didier Drogba on Liam Ridgewell, free kick awarded. Ben Foster restarts play with the free kick.21:33
James Morrison takes a shot from deep inside the box clearing the bar.21:23
Michael Essien delivers the ball, clearance by Jonas Olsson.20:09
Outswinging corner taken right-footed by James Morrison, Petr Cech makes a save.20:00
The ball is sent over by Marc-Antoine Fortune, David Luiz manages to make a clearance.19:33
Jerome Thomas fouled by Ramires, the ref awards a free kick. Direct free kick taken by Liam Ridgewell.18:57
Peter Odemwingie produces a right-footed shot from the edge of the box and misses to the left of the goal.18:38
James Morrison takes a shot. Michael Essien gets a block in.17:19
The ball is swung over by Liam Ridgewell, Marc-Antoine Fortune produces a right-footed shot from the edge of the box and misses to the left of the goal.14:42
Peter Odemwingie is caught offside. Indirect free kick taken by Gary Cahill.14:16
Michael Essien takes a shot. Gareth McAuley gets a block in.13:57
Inswinging corner taken left-footed by Juan Mata, Gareth McAuley makes a clearance.13:41
Juan Mata takes a shot. Save by Ben Foster.13:15
A cross is delivered by Marc-Antoine Fortune.11:27
A cross is delivered by Juan Mata.11:22
Daniel Sturridge delivers the ball.10:02
James Morrison sends in a cross, Gary Cahill makes a clearance.8:32
Peter Odemwingie produces a cross.7:38
Corner taken right-footed by James Morrison from the right by-line, save by Petr Cech.7:21
James Morrison takes a shot. Petr Cech makes a save.6:47
Keith Andrews takes a shot. Blocked by Michael Essien.5:58
Free kick awarded for a foul by Frank Lampard on Jerome Thomas. James Morrison crosses the ball from the free kick right-footed from right wing, Didier Drogba makes a clearance.5:29
Juan Mata produces a cross, clearance made by Gareth McAuley.5:05
Juan Mata takes the inswinging corner, Keith Andrews makes a clearance.2:16
Liam Ridgewell sends in a cross.2:08
The ball is swung over by Steven Reid.1:35
Didier Drogba is caught offside. Ben Foster restarts play with the free kick.0:53
Foul by Liam Ridgewell on Daniel Sturridge, free kick awarded. Direct free kick taken by Daniel Sturridge.0:00
The match begins.
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