Last Updated: 02/03/13 4:54pm
Despite the best efforts from Olsson inside the box from the corner, and some acrobatics from Foster, the Blues hang for the three points.
Mata takes a slow march off the field to allow John Obi Mikel to take to the park for the final moments of the match.
Rosenberg spots Odemwingie out o the right of the box and finds him with ease, but the latter's strike to the near post is smothered by Cech.
Chelsea seemingly limping their way over the finish line, Albion throwing everything at them in the final third.
Lampard spots Moses out on the right and finds him with a good ball, but the Nigerian's return into the box is below-par and is cleared by the defence.
A lovely one-two from Oscar and Mata allows the latter to get in behind the defence, but his initial touch is too heavy andFoster has the time to drop low and smother.
Oscar goes down on the left and looks for a foul, but the referee waves play on and the Baggies make their way up field with some zeal.
Could Fernando Torres come and rescue Chelsea from the late fightback from West Brom, the Spaniard replacing Ba.
Entering the last five minutes of regulation time and one can sense the home fans are nervous with Albion pushing up.
Moses wasted a shot on goal at the other end, but it's worrying times for Benitez's men as Albion press up determinedly in the final ten minutes.
Good left-handed save to his right by Cech denies Odemwingie from the set-piece, with the Blues gloveman up to the task from the subsequent corner-kick moments later.
Mata gives away a good free-kick for Albion on the right after Odemwingie is adjudged to have been fouled. Meanwhile, Yacob is removed with Markus Rosenberg coming on in his stead.
Oscar wriggles through and engineers a shot on goal, only for Foster to once again thwart to the Blues forward.
The numbers game catches up with Mata down the right flank, with Victor Moses taking to the pitch in place of Hazard.
Oscar gets some decent power behind his shot, but Foster does as well to get behind the ball and smother the stinging drive.
No danger to Chelsea from the subsequent set-piece, with Olsson eventually giving away a free-kick for a tackle on Lampard.
Morrison delivers the ball to the far post for McAuley, but the ball is bumbled into touch for a corner.
A certain spell of pressure from Albion as they get another corner, this time from the left. The ball is headed out to Olsson, who takes a pot-shot from the edge of the box but way over the bar.
Olsson is bundled over as he looks to get on the end of Dorrans' delivery, whose set-piece take is his final contribution of the match with Jerome Thomas taking his place.
Baggies now asking a few questions on attack as they earn themselves a corner-kick, with Dorrans lining up to deliver from the right.
Ba, once more, is blocked, this time out on the left, after a sweeping attack from Chelsea with Ivanovic even pushing up in earnest.
Too skillful, and too pacy from Hazard for McAuley to deal with as the Baggies defender gives away a free-kick on the edge of the area.
Mata gives away the ball on the halfway line, but Albion struggle to build up enough head of steam from the good fortune.
Dorrans ball into the are from the left is easily headed clear by Lampard, not that there were many Baggies in the box.
Sloppy passes in midfield letting Albion down as they loses possession on the halfway line. Some strong defence from Olsson sheperds the ball off Hazard, who goes down in the box, but no penalty for the hosts.
Mata trying to create a bit of magic out on the left wit hOsacr, the former finally drifting into the box, only to tap the ball too far forward and loses possession.
Mata finds Oscar out on the right, but the Blues ace is well-marked and his return pass is weak and easily gathered up by the defence. Meanwhile Hazard picks up thefirst caution of teh match for a stray boot on Olsson.
Ba improvises well to still get a shot off on goal off yet another Chelsea corner-kick, as Albion's defence just about clears the danger.
Dorrans tries to get behind Azpilicueta down the left flank, but instead gives away a free-kick for knocking over the Blues full-back.
Albion hurried off the ball as Lampard eventually tucks it into the back of the net after a good attacking movement, but the flag is up for offsides.
Azpilicueta's ball from the right is easily gathered by Foster. Moments later, and Chelsea are pressing again, Ba this time turning and shooting, but his effort is blocked.
Oscar's ball from the left is cleared, but the Brazilian and Cole are combining well down the flank early on.
It's early going in the second period, but Chelsea clearly look eager to double their lead as Mata scuffs his shot on goal.
Baggies have started too slowly again - too much sitting behind the ball, inviting Chelsea onto them. Dave
Is it me or is Rafa becoming the new tinkerman with less personality or likeability, here's hoping Frank gets his 200th today COYB Paul Anderson
Good luck chelsea! Get back where we belong, top 3. Also dont sweat your self before the europa league game - Jas Vig
So far, so good for Benitez's men as they make their way towards the changing rooms a goal to the good for their first half efforts.
Yacob giving away another silly free-kick for a sloppy challenge on Mata: the Baggies man best have a chat from Clarke at the break for his overzealousness.
An unmarked Long in a great position inside the area, but Youssouf Mulumbu's pass is deflected and snatched up by the defence.
Long's ball from the right is for Morrison inside the area, but the latter was covered as the pass sails over his head.
A very rare attempt at goal from the Baggies as Morrison takes aim at goal, but his effort keeps rising away from Cech and the crossbar.
Albion looking a little directionless going forward and maybe need a stiff talking form Clarke at the half-time break.
Successive shots from Oscar and Cesar Azpilicueta just inside the box that the Baggies defence throw bodies at the block and then clear.
Oscar's shot on goal is cleared into touch by Ridgwell, but the Blues fail to capitalise on their sixth corner of the match.
Cole gives away possession out on the left, the England full-back not having the best of performances thus far after earlier getting caught off guard by Dorrans near the box.
Good control from the hosts at the back to secure possession off Albion and work the ball back up the park.
Mata looking for Ba out on the left, only for the ball to be headed clear. The ball is eventually worked back to the goalscorer, whose shot on target is too weak to trouble Foster.
Oscar going for the spectacular trying to connect with Hazard's ball into the box from the right as Olsson hacks it clear.
It's going to take a lot for Albion to pull back on level terms after rarely pushing up since the opening whistle.
Mata, again, fancies a pop on goal as Foster is alert to the danger and gets low to smother the attempt.
Chelsea were good value for their goal, but it was David Luiz's earlier free-kick take that draw a fine save from Foster that started it all.
GOAL! A deserved goal for Chelsea as Ba gets in behind Gareth McAuley and it's a simple finish for the Senegalese hitman.
A very bright start from the Blues, who playing at a good tempo and creating chances. Oscar earns his side a decent free-kick after Claudio Yacob clatters into him.
Mata's ball into the box nearly finds the feet of Hazard who held his run, but the Foster is sharp to make the clearance.
Real disciplined shape to the Baggies defence that is proving a real bother for the Blues to break down.
Mata tees up Oscar on the edge of the box out on the left, but the young attacker's shot is wide to the right of goal.
Ashley Cole's ball from the left looks to be a threat with Oscar waiting in the 18-yard area, but the defence clears the danger.
Lovely touch from Ba on the left for Mata, with the Spaniard earning the Blues their third corner of the match.
Nothing coming from the set-piece for the hosts, but the back working the ball from the back. Ba eventually getting an opportunity to shoot, but once it's a comfortable gather for Foster.
Blues on the break, with Mata getting time on the ball out on the right to deliver a decent ball for Oscar, whose header on goal is pretty tame and straight at Foster.
The visitors working the left flank, with Shane Long the target man, but the home side force the movement back over the halfway line.
Hazard breaks away down the right but is blown up for a studs-up challenge for teh ball on Liam Ridgewell.
Albion trying to get something going on the attack, but Steve Clarke's men are being pushed back by the high-line of the Blues.
Ba and Oscar pushing up into the final third doggedly as they look to keep the pressure on the defence.
The Blues breakout from inside the own half of the pitch through Mata and Oscar, but Albion's defence manages to track back in time to poach possession.
James Morrison goes down under the challenge of Ramires and the Baggies get a free-kick in a good area from out in front.
Good positive play from Chelsea as Oscar taps the ball back in the path of Juan Mata to take a shot at goal that is just off target.
Great ball from the right by Demba Ba for Oscar in a good area, but the Brazilian's shot is well saved by Foster from close-range.
The hosts passing the ball around positively enough, with Branislav Ivanovic pushing up towards the halfway line to increase the bodies going forward.
Searching ball into the box from the right from Eden Harzard for Oscar, but it just has too much pace on it and bounces comfortably into Ben Foster's hands.
Not sure about this one. Rafa is running out of time and a bad performance here could spell the end of him. I'll go for a 3-1 win for Chelsea with Torres coming off the bench to get one, Lampard to get the other 2 and Long to get the one for West Brom. COYB! Michael Dingle
Another Benitez team shuffle. And he reckons the supporters are to blame for our form! Just pick your best side and the results will follow!Who knows if we'll win today. I'm hoping we'll do it. 2-1 maybe? Julian Catt
Hi, CHELSEA to win today with a 2-1 victory! Ba to score first then Mata. Always supporting the blues and GOOD LUCK! To the team!!! From Toby Day
Frank Lampard makes his 592 appearance for Chelsea and he is at par with John Hollins as Chelsea's third highest appearance maker. Here'shoping he gets his 200th goal as well. Super Frankie Lampard. Best, Madhurima Basu (India)
Feel free to e-mail your thoughts or predictions to firstname.lastname@example.org and we'll publish as many of them before - and during - the game as possible.
The Baggies welcome back striker Shane Long, who limped off against the Black Cats, Lukaku cannot face his parent club and will miss this clash. Left-back Goran Popov is still serving his red card suspension and will only be eligible to play after the weekend's encounter.
Benitez makes a few changes to the side that disposed of Boro on Wednesday, Paulo Ferreira, Ryan Bertrand, Nathan Ake, Victor Moses and Yossi Benayoun among those to make way as Ashley Cole, David Luiz, Frank Lampard, Eden Hazard and Demba Ba return to the starting line-up. Defenders Gary Cahill and Cesar Azpilicueta missed the midweek tie due to illness and injury respectively, with the latter back in the run-on side while the former starts off the bench.
West Brom are rated at 7/1 to beat Chelsea today according to our friends at Sky Bet, while it is 7/2 for the match to end in a draw. Fernando Torres is 4/1 to score first and 25/1 to secure a hat-trick, while Frank Lampard is 5/4 to find the back of the net before the final whistle.
Meanwhile, the Baggies make the trip to the capital on the back of a 2-1 win over Sunderland last time out, with on-loan Blues forward Romelu Lukaku on target for a brace. Steve Clarke's men remain a challenge to more fancied sides this season, as their seventh place standing bares testament.
The Blues swept aside Middlesborough in midweek to progress to the next stage of the FA Cup, yet it was interim boss Rafael Benitez's outburst following his side's win that grabbed all the headlines. But with the west London outfit in fourth place on the Premier League table, the Spaniard remains - for the time being - focused on improving their finish by the end of the season.