The midfielder was promptly substituted and referee Anthony Taylor was barracked by Chelsea players and supporters thereafter.
The Blues are unbeaten in six games since the departure of Jose Mourinho, but Guus Hiddink’s hopes of a top-four finish receded further in front of owner Roman Abramovich and ahead of Saturday’s clash with Everton.
Chelsea began well. Costa glided by Jonny Evans but shot wide and Willian fired off target either side of McClean heading off target from Darren Fletcher’s cross.
James Morrison departed with an apparent hamstring problem before Azpilicueta blocked a Fletcher effort and then scored at the other end.
Azpilicueta is less than prolific, but likes scoring against West Brom.
The full-back, who netted at The Hawthorns in August, claimed his first goal at Stamford Bridge when he prodded in Branislav Ivanovic’s cross at the back post.
There were holes aplenty in the visiting defence, but Chelsea’s rearguard was porous too.
The Baggies breached and exposed when Pedro gave the ball away to Fletcher, who was influential for the visitors.
Fletcher prodded it to Gardner, who did the rest, shooting into the bottom corner from 25 yards.
Costa ballooned an effort over and Salomon Rondon shot just wide as both sides had chances to take an interval lead.
Pedro made his debut at The Hawthorns and inspired Chelsea to a first win of the season, but his star has faded since.
The subdued Spain winger was withdrawn for Kenedy at half-time and the Brazilian gave Chelsea much-needed pace and penetration in an increasingly disjointed contest.
Costa had no complaints when he was booked for a poor lunge on Gardner after losing control of the ball.
Kenedy next powered down the left and Costa looked to join the attack, only to tumble in front of Yacob.
The Baggies midfielder avoided punishment, prompting Chelsea complaints led by captain John Terry. Yacob did go off, substituted for Saido Berahino.
Chelsea continued to press, with a deflected Costa effort going into the side-netting.
McClean was then booked for squaring up to Thibaut Courtois as the contest became more niggly still.
Chelsea took the lead for a second time when Willian’s cross deflected in off McAuley, who was under pressure from Kenedy.
Costa was denied and Kenedy shot wide before McClean equalised from the edge of the area after Chelsea twice failed to clear.
MANCHESTER CITY 0, EVERTON 0
Raheem Sterling was controversially denied a late penalty as Manchester City were held to a frustrating goalless draw by Everton.
Sterling went down under a challenge from John Stones in injury time but referee Roger East gave nothing and City dropped two points in the Barclays Premier League title race.
City had dominated proceedings on a wet and cold night but were continually frustrated by the dogged visitors, for whom goalkeeper Tim Howard was outstanding.
City striker Sergio Aguero also had a couple of penalty appeals turned down as City, a week after losing at Goodison Park in the Capital One Cup, once again found Everton a tough nut to crack.
The major talking point prior to the game was the traffic problems on the motorway network around Manchester which delayed many supporters. The ground was not full at the scheduled 7.45pm start and the Everton team had even arrived later than planned, although not severely. People continued to trickle into the ground throughout a lively first half.
Injury to Seamus Coleman meant that Everton lined up with Stones at right-back but with Phil Jagielka back from injury in the centre, the back four was not particularly weakened. City left playmaker David Silva on the bench and operated with Sterling behind Aguero and Jesus Navas and Kevin De Bruyne either side.
City pieced together a slick early move as Sterling played in De Bruyne but the Belgian shot wide. Yaya Toure also tested Howard with a firm header.
Aguero claimed he was tripped by Mohamed Besic when clean through but referee East gave nothing and Sterling fired over.
At the other end, Nicolas Otamendi almost turned the ball into his own net as he stretched to cut out a Gerard Deulofeu cross while Leon Osman went close to a spectacular opener as he volleyed a Romelu Lukaku cross narrowly wide.
City started the second half brighter but Everton defended doggedly and frustrated the hosts. Sterling failed to make firm contact in front of goal, Aguero hit the side-netting and Toure had an effort deflected over.
Aguero did meet a De Bruyne corner with a firm shot but Howard was in the right position to palm away and the American then stretched out a boot to deny Sterling.
Howard did even better to spread himself and block from Aguero again after the Argentinian had shrugged off countryman Ramiro Funes Mori, although the City man felt he had a penalty claim against the defender.
City sent on Silva for the final 16 minutes in the hope of prising an opening but the visitors survived as Navas headed wide and Aguero wriggled through but missed the target.
There was late drama as Aguero went down trying to beat two defenders but his appeal seemed optimistic. Sterling’s penalty claim seemed stronger, and fans thought East had pointed to the spot, but instead it was merely a goal-kick.
SOUTHAMPTON 2, WATFORD 0
Southampton impressively outplayed and outworked Watford to secure a 2-0 Barclays Premier League victory that should signal the end of their poor run.
On an evening when Watford were as poor as the hosts were intense, goals in each half from Shane Long and Dusan Tadic took Southampton into 12th place and within two points of their underwhelming visitors.
Ronald Koeman began with a 3-5-2 formation – and with Ryan Bertrand one of his central defenders – and with England international goalkeeper Fraser Forster returning from a long-term knee injury.
Throughout much of their disappointing recent run – they had lost eight of their previous 10 fixtures – Southampton had begun games encouragingly before their confidence deteriorated upon harshly conceding the opening goal or not converting their chances.
It therefore came as little surprise that they were the more energetic of the two teams immediately after kick-off, even if the reality is their opening goal arrived when the threat appeared minimal.
Matt Targett, playing as a wing-back, received possession on the left wing before curling an accurate, 17th-minute cross into the penalty area towards Long – from where the forward neatly headed beyond goalkeeper Heurelho Gomes and inside the right post.
Watford’s response was to become even more sluggish, and erratic, and to allow Sadio Mane to run near-unchallenged from the left wing and to the edge of the penalty area before shooting and watching Gomes palm his effort wide.
From the resultant corner, Targett – demonstrating his team’s growing confidence – shot from distance before watching the ball being deflected off-target, and while Odion Ighalo provided an isolated response with a run and shot that was also deflected, the hosts otherwise remained in control.
The concern remained that with Watford’s talent a one-goal lead would not be enough, and had they secured an equaliser, Mane – more than any other – would have felt responsible. After intercepting a rare misplaced pass from Jose Jurado, the forward found himself immediately in front of goal but instead struck the outside of the post.
This was the worst performance the otherwise-impressive Quique Sanchez Flores has overseen since his appointment as Watford’s manager, and he will know that had Mane not missed further chances, and Steven Davis’ classy finish not been ruled offside, his team would have lost more heavily.
Pressure had been building on his counterpart, Koeman, but as if to highlight Southampton’s poor run had reached its conclusion and that he remained firmly in control, the manager substituted Mane for Dusan Tadic and was almost instantly rewarded with a goal.
Controlling possession after Davis’ header, Tadic ran into Watford’s penalty area, created space, and classily finished low beyond Gomes from in front of goal in the 73rd minute.
In doing so, a crucial victory was secured, and unlike in the 4-0 defeat of Arsenal, this time winning appeared far from a one-off.
SWANSEA CITY 2, SUNDERLAND 4
Jermain Defoe struck a hat-trick as Sunderland won a thrilling Barclays Premier League relegation battle at Swansea.
The Black Cats’ 4-2 victory was mired in controversy as they recovered from a 2-1 half-time deficit to claim a second successive league win and provide real hope of avoiding the drop.
Sunderland’s victory took them above neighbours Newcastle on goal difference and within a point of Swansea, who were reduced to 10 men when Kyle Naughton was sent off close to half-time with the score 1-1.
Graham Scott, a late replacement for Andre Marriner on Monday, was taking charge of only his fourth top flight fixture – and the Oxfordshire official was in the spotlight most of the night with several big calls to make.
Defoe’s first two goals despite him being perilously close to offside on both occasions, while Scott awarded Swansea a first-half penalty which appeared generous in the extreme – then sent off Naughton in contentious fashion.
Sunderland were gifted the perfect start after three minutes when Lukasz Fabianski’s loose ball was collected by Adam Johnson and his pass found Fabio Borini.
The former Swansea striker’s shot was too hot for Fabianski to hold and Defoe was on the spot to tap into an empty net to score against the Welsh club for the third consecutive game.
Swansea were visibly shaken and it almost got worse when Patrick van Aanholt raided down the left to deliver a cross which the unmarked Johnson sent carelessly wide.
Had that gone in it might have been a long way back for a Swansea side, who had started the evening as the joint-lowest scorers in the Premier League.
But they were handed a lifeline after Andre Ayew provided proof that he was in the mood by meeting Gylfi Sigurdsson’s corner and flashing a header just wide of the post.
Three minutes later the Ghanaian broke into the box and won a dubious penalty decision after appearing to kick the floor in the act of shooting.
Wes Brown was adjudged to have made the most marginal of contact, but Sigurdsson stroked home the penalty with the minimum of fuss.
Swansea were reduced to 10 men when Naughton was punished for a 37th minute challenge on Yann M’Vila, his studs showing but the defender clearly took the ball and the theatrical reaction of the France international did him few favours.
However, Ayew almost instantly sprinted into space, shrugged off Lee Cattermole and buried a powerful low shot through the legs of Billy Jones and into the far corner of the net.
Swansea manager Alan Curtis instantly withdrew Leon Britton on the occasion of the midfielder’s 500th appearance for the club as Angel Rangel filled Naughton’s right-back position.
But Sunderland were level four minutes after the restart as van Aanholt’s drive took a telling deflection off the back of Federico Fernandez and flew past Fabianski off a post.
Jermain Lens struck a post from a tight angle as Sunderland came on strongly and Defoe put them ahead just after the hour when he was adjudged onside from Johnson’s pass and finished expertly.
Rangel was not so fortunate when he bundled the ball home after Vito Mannone had spilled Sigurdsson’s deflected shot on his goal-line.
And Sunderland wrapped up the points when Defoe was again in the right place to finish van Aanholt’s cross from a few yards out four minutes from time.
STOKE 3, NORWICH CITY 1
Norwich proved instrumental in their own downfall as they succumbed to a 3-1 Barclays Premier League defeat at Stoke.
With the score at 0-0, the Canaries were reduced to 10 men in the 31st minute when Gary O’Neil was sent off for an utterly needless slide tackle on Ibrahim Afellay.
After then falling behind to Jonathan Walters’ 49th-minute effort, Norwich did well to level six minutes later through a cracking Jonny Howson strike.
But Stoke regained the lead via Joselu’s smart finish in the 67th minute, and the away side then shot themselves in the foot again as Ryan Bennett’s own-goal 12 minutes from time sealed victory for the hosts.
Norwich remain five points clear of the relegation zone in 15th place, but will be disappointed with their efforts here after registering three wins in their previous four league fixtures.
The Potters, meanwhile, now have three victories from four top-flight games themselves and are up to seventh.
Stoke – with most of the players rested for Saturday’s FA Cup game back in their side, but not hamstring injury victim Xherdan Shaqiri – made a positive start to the contest.
Marko Arnautovic brought a decent save out of Declan Rudd having received a fine lofted pass from Joselu, who was then just unable to finish on the stretch as the same Potters pair combined again.
Howson sent Norwich’s first real effort into the stand, before both Walters and Joselu put the ball wide from Arnautovic tee-ups.
The home side seemed in control, but they survived a scare when Wes Hoolahan collected the ball direct from a poor Jack Butland kick only to send it wide.
Butland then quickly redeemed himself, pulling off a great diving stop to push away Bennett’s strike.
Moments later, Norwich found themselves a man down in baffling circumstances after O’Neil opted to make a lunging tackle from behind on Afellay, despite the ball having already more or less run out of play in front of them down by the dugouts.
The challenge absolutely clattered Afellay and left referee Neil Swarbrick with little option but to produce the red card for O’Neil.
Walters looped a shot over the bar, then Arnautovic completely miss-kicked in a decent position as Stoke looked to make their man advantage count.
And soon after the break it was that duo who fashioned the opener, Arnautovic whipping in a delightful cross that Walters tucked away with the visitors’ defence static.
Things looked grim for Norwich, but the 10 men then shocked their hosts with a swift and emphatic response as Vadis Odjidja-Ofoe chested a Hoolahan cross down on the edge of the box and Howson lashed into the corner.
Canaries boss Alex Neil looked eager to seize the moment as he sent Matt Jarvis and Nathan Redmond on not long after, but within only a few minutes of that, Stoke’s lead was restored, Sebastien Bassong’s attempt at a clearance only coming to Afellay, whose pass was slotted in coolly by Joselu.
Bennett then inadvertently made the points safe for the opposition, nodding Afellay’s free-kick past Rudd, who did well late on to deny Stoke substitute Peter Crouch.