Chelsea were controversially denied a late penalty as they were held to a 1-1 draw by West Ham at the London Stadium to leave their top-four hopes hanging by a thread
Conor Gallagher's low shot struck Tomas Soucek on the hand as the West Ham midfielder slid across in an attempt to make a block in the 88th minute, but referee Craig Pawson waved away their appeals and there was no intervention from VAR
Earlier, Graham Potter's new-look side had started strongly and looked like they might subject the hosts to a punishing afternoon when January signings Enzo Fernandez and Joao Felix combined for the latter's first Chelsea goal (16) on his return from suspension
But West Ham weathered the early storm and capitalised on poor Chelsea defending when Jarrod Bowen flicked on Vladimir Coufal's cross, allowing the unmarked Emerson to turn home at the far post (28) against his former side
Chelsea, held to goalless draws in their previous two games, once again struggled to break their opponents down after that and West Ham thought they had won it late on when Soucek scored from close range, only for VAR to rule it out for offside
But the biggest flashpoint was still to come as Chelsea were denied a penalty despite Gallagher's effort, struck from the edge of the box, clearly striking the Czech Republic midfielder on the hand, with Potter jokingly describing it as a "good save" in his post-match press conference
The draw leaves the Blues in ninth place, nine points behind fourth-placed Newcastle, and piles more pressure on Potter
 West Ham, meanwhile, remain 15th and extend their unbeaten run to four games in all competitions
Chelsea came into the game having failed to score in over three hours of Premier League action but it looked like they might finally have clicked in the early stages at the London Stadium
In fact, Felix had already had the ball in the net once before his opener, seeing an effort ruled out for offside having raced onto a through-ball soon after West Ham's Lucas Paqueta had suffered a suspected dislocated shoulder
Paqueta was duly substituted for Soucek and Chelsea's breakthrough came soon after the enforced change, Felix finding himself with time and space to convert from Fernandez's teasing cross
Chelsea looked like they might run away with it at that point, their new-look front line of Felix, Mykhailo Mudryk, Noni Madueke and Kai Havertz combining dangerously as Fernandez pulled the strings from the base of midfield
Havertz had another goal ruled out for offside after finishing smartly from Mudryk's reverse pass, but West Ham hung on and then punished slack Chelsea defending to level when Emerson popped up at the far post to score against his former club
West Ham had gone close shortly before that, when Michail Antonio's flicked effort from Bowen's cross was blocked by Kepa Arrizabalaga, but Chelsea then created a series of other chances before the break, with Madueke forcing a fine save from Lukasz Fabianski
Rather than pick up where they left off, however, Chelsea's attacking threat faded badly, with Felix unable to replicate his influential first-half showing and West Ham growing in stature
Potter's side created a couple of half-chances, with a Reece James free-kick flashing wide off the top of Antonio's head, and Havertz heading wide from a centre by substitute Ben Chilwell
But West Ham held firm and the London Stadium erupted in celebration when Soucek bundled home from a free kick after Declan Rice's initial effort had been saved, only for a lengthy VAR check to correctly rule the goal out for offside
There was no such VAR check for Chelsea, however, when Gallagher's effort struck the hand of Soucek, referee Pawson waving play on and forcing Potter and his players to once again settle for a point
Chelsea head coach on Soucek's handball: "It was a good save - you need your goalkeeper to help get you the points
"It hasn't been given so there is nothing for me to say
 If it was given, it wouldn't have been overturned but it hasn't been given
"It looked a handball to me
 I didn't know Tomas [Soucek] could get down that quickly to make a save like that
 It's a good stop from him
"It's not for me to say about VAR
 They are human beings
 When there is a different human being in the room, so every single decision and action means you won't get the same one again
"It's very hard to get consistency
 Some go for you, some don't
 You have to accept that
"Of Chelsea's performance, he added: "I felt today was a step forward performance-wise
 We started the game well
 You are always rocked by the goal as that's football - we must learn from that
"We've had a good training week but when you don't get the three points there is stuff you can do better
"Felix looked like a man making up for lost time in the first half
 The Portuguese international had waited long enough, after all
 More than a month had elapsed since his red card against Fulham on his debut
Felix was outstanding in that game, at least he was before the moment of madness that earned him his three-match suspension, and he picked up where he left off against West Ham, finding space between the lines and wreaking havoc early on
There was slick combination play with Mykhailo Mudryk on the left and he popped up on the opposite flank too, feeding team-mates and at times running in behind West Ham's defence himself
His goal was smartly taken, finished first time from Enzo Fernandez's diagonal cross, and he had the ball in the net before that too, only for the offside flag to deny him on that occasion
His influence waned in the second half, the 23-year-old perhaps still needing to adapt to the intensity of the Premier League, but overall he showed enough to make him the game's outstanding performer, his importance reflected in the fact that Potter kept him on until the end as others were withdrawn
Chelsea's sluggish second-half performance showed familiar issues under the head coach
 Their top-four hopes continue to fade
 But Felix's performance was a bright spot
 He is sure to be central to any upturn in form
West Ham boss  said: "I've got to give great credit to the boys for coming from behind
"We didn't look right [at the start] and I have to say early on that Declan Rice played with a virus today, which you could probably see in his performance, his level was a little below where he'd normally be, but after 20 minutes I'd have shook your hand and taken a draw after the way we started
"Defensively we weren't good today, but the only thing was we kept ourselves in it
 We didn't concede a second goal, which would have made it difficult to get back
"We worked our way into the game, it took us 20 or 30 minutes to get into the game, but as it went on I thought we got a bit better
"In the second half especially we gave them more of a game and it was a bit more for sharing after half-time
"On the Soucek handball, he said: "I've not seen it
"have another London derby next weekend when they visit  on Sunday 19 February; kick-off 4
30pm, live on 
face  in the first leg of their Champions League last-16 clash at Stamford Bridge on Wednesday 15 February - kick-off 8pm - before they host  back in the Premier League on Saturday 18 February; kick-off 3pm
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