Timo Werner's first-half strike helped strengthen Chelsea's grip on the top four with a 1-0 win at West Ham, who saw Fabian Balbuena controversially sent off after a VAR intervention.
Chelsea's winner came just before half-time through Werner's first Premier League goal since mid-February, finishing off at close range from Ben Chilwell's low cross (43).
The game opened up in the second half as Werner missed a fine chance to double his tally, turning wide at close range from a rebound, and West Ham were reduced to 10 men with a baffling dismissal as Balbuena's studs caught Chilwell's calf after following through with a clearance.
After referee Chris Kavanagh consulted the pitchside monitor to view the incident, which seemed an unavoidable action from the West Ham defender, Balbuena was shown a red card.
Chelsea saw the game out, meaning Thomas Tuchel's side are fourth, now three points clear of fifth-placed West Ham, with Liverpool a further point behind in sixth with five games remaining.
- Premier League table: Chelsea three clear of West Ham
- How the teams lined up | Match stats
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West Ham: Fabianski (7), Coufal (6), Balbuena (5), Diop (6), Ogbonna (6), Fredericks (5), Noble (6), Soucek (6), Fornals (6), Lingard (6), Bowen (5)
Subs: Benrahma (6), Lanzini (6), Johnson (NA)
Chelsea: Mendy (6), Rudiger (7), Silva (7), Christensen (7), Azpilicueta (7), Kante (7), Jorginho (7), Chilwell (6), Mount (8), Pulisic (6), Werner (7)
Subs: Ziyech (6), James (NA), Abraham (NA)
Man of the match: Mason Mount
How Werner dealt a hammer blow in top-four race
West Ham's surprise top-four challenge this season will have no doubt strengthened desires for the 'big six' to breakaway to an exclusive European competition, with these two sides arriving on equal points with just six games remaining.
Chelsea had some joy down the right early on as Werner turned Mason Mount's cross over the bar from 12 yards, before Christian Pulisic struck Werner's own low centre into the hands of Lukasz Fabianski.
Chelsea had all of the ball, as expected, but were shut out by West Ham, who were keen to soak up pressure and counter-attack at every opportunity; in every home game against top-half opposition, David Moyes' side have had less than 40 per cent possession.
But Chelsea scored against the run of play in a move started and finished by Werner, who now has 20 goal involvements (11 goals and nine assists) this season, more than any other Blues player.
Receiving the ball with Angel Ogbonna on his back, Werner held it up well and found Pulisic, who spread out wide to Chilwell. The German then continued his run into the box and slotted home Chilwell's low cross from eight yards with just two minutes of the first half remaining.
But Werner missed a huge chance to put Chelsea 2-0 up early in the second half; after Mount's long-range effort was saved by Fabianski, the ball fortuitously fell into Werner's path, six yards out, but he skewed his effort wide of the post with just the goalkeeper to beat.
West Ham were then jolted into life as Ryan Fredericks' goalbound effort was blocked well by Mount, before Jesse Lingard's clever half volley floated just wide of Edouard Mendy's left-hand post.
West Ham made two changes in defence, with Fabian Balbuena and Ryan Fredericks replacing Ben Johnson and the suspended Craig Dawson.
Chelsea made six changes from the goalless draw against Brighton, meaning they have now made a joint-high 111 Premier League changes this season, level with Man City.
As expected, Edouard Mendy replaced Kepa Arrizabalaga in goal, while Reece James, Kurt Zouma, Marcos Alonso, Hakim Ziyech and Kai Havertz also dropped out. They were replaced by Cesar Azpilicueta, Thiago Silva, Ben Chilwell, N'Golo Kante and Timo Werner.
Mount was fantastic once again for Chelsea, forcing another fine save from Fabianski with a long-range effort with little backlift, but the visitors began to retreat as the game wore on to protect their lead.
West Ham's task was made more difficult, however, when Balbuena's seemingly innocuous collision with Chilwell was referred to VAR and then the pitchside monitor.
Clearing the ball, Balbuena's foot caught the leg of Chilwell, who was closing down the West Ham man, and slowed down, the incident looked far worse than it was.
Kavanagh dismissed Balbuena, a decision David Moyes described as "rubbish" and "made by somebody who has never played the game," and though West Ham pushed to find an unlikely equaliser, they were restricted to long-range efforts.
Sub Tammy Abraham missed a clear header from close range for Chelsea in the final minute of stoppage time, but it did not matter as Tuchel's positive impact continued, this their 16th clean sheet in 20 games under the German.
Pundits: Not even a yellow!
Danny Gabbidon on Sky Sports:
"It's not even a yellow for me. This totally killed the game. He turns, clears the ball upfield, what is he supposed to do? There can be contact and it not be a foul for me.
"I'm not sure you can blame VAR for that. The VAR has flagged the incident, it's then down to the ref to make the right decision, and for me he gets that totally wrong. He's just clearing the ball up the line. What is he supposed to do? He can't move his foot in a different direction, it's impossible."
Gianfranco Zola on Sky Sports:
"You cannot believe that. It can happen that the referee makes a mistake if he only sees the end of it, but the VAR should be in control of the situation and see it is not an intentional foul. West Ham didn't deserve it. It was totally unfortunate."
What the managers said...
West Ham boss David Moyes on Balbuena red card: "I think it's a decision made by somebody who's never played the game. I don't know where Fabi Balbuena is supposed to plant his foot.
"If they do think that, you'll look at the one a few minutes later, with Coufal and Rudiger, a similar challenge, but they never did anything about it.
"I don't know how it's a red card. I don't know where he's supposed to plant his foot. I don't think for one minute there's a bit of malice in that. I thought it was a rubbish decision.
"We'll go again, we're in a decent position. There's games to play, hopefully we're right in the mix for some form of European football 'til the end, and I'll keep pushing to make that Champions league if we can."
Chelsea boss Thomas Tuchel: "The boys are very, very happy in the dressing room, and they can be. Great performance and amazing result, I think a well-deserved win for us.
"Very tough to play [at West Ham], you can win ball possession, but you have to earn your chances, and be very, very smart. You cannot afford to do easy mistakes and you have to be patient.
"It was a pretty normal preparation, we did not talk one word about Super League from Tuesday on. I felt everyone was very concentrated and enjoying the focus on just the game. I am happy that we came up with an intense performance."
On Timo Werner: "He always gives everything. He could have made it more comfortable, but very happy because he played a very good match."
- West Ham have lost four of their last eight Premier League matches (W3 D1), as many as in their previous 23 matches in the competition (W13 D6 L4).
- Chelsea manager Thomas Tuchel is unbeaten in all 10 away matches with the Blues (W8 D2) and is only the second manager in Premier League history to remain unbeaten in his first 10 away games in all competitions with a club, after Claudio Ranieri with Leicester City in 2015 (unbeaten in first 11).
- Since Thomas Tuchel's first Premier League game in January, only Manchester City (36) have won more points in the competition than Chelsea (29).
- This was Chelsea's 10th clean sheet in just their 14th Premier League match under Tuchel, equalling the quickest a manager has recorded 10 clean sheets in Premier League history.
Live Premier League
West Ham now go to Burnley on Monday Night Football on May 3, live on Sky Sports Premier League.
Chelsea go to Real Madrid in the first leg of their Champions League semi-final on Tuesday at 8pm, before hosting Fulham on Saturday Night Football on May 1 at 5.30pm, live on Sky Sports Premier League.