West Ham secured their first Premier League win at the Emirates Stadium since 2015 and damaged Arsenal's title hopes with a surprise 2-0 London derby victory on Thursday evening.
A calamitous scramble in the Gunners box ended when Tomas Soucek arrived to belt in the opener before Konstantinos Mavropanos flicked in James Ward-Prowse's corner to double the Hammers' lead.
Arsenal could not muster a response despite the likes of Leandro Trossard, Bukayo Saka and Gabriel Jesus having good opportunities, allowing Liverpool to grow a two-point lead at the top of the table at the conclusion of Gameweek 19.
How the game unfolded
West Ham showed threatening signs early on as Ward-Prowse fired goalwards from 20 yards, his effort just soaring over David Raya's goal.
Nice work from Ben White, Declan Rice and Martin Odegaard helped Mikel Arteta's side fashion their first major opening with the ball falling to Bukayo Saka, but the England winger's effort was fired disappointingly straight at Alphonse Areola.
While firmly against the run of play, West Ham's rugged approach which also saw them win at fellow north London side Tottenham rewarded them as indecision in the home box provided Soucek with a chance on goal.
Emerson Palmieri's cross hit two defenders and deflected to Jarrod Bowen, who showed his presence of mind to lay the ball back to Soucek who rattled in confidently inside the box. The VAR check took unnecessarily long as checks were made on the ball staying in the field of play, but it was eventually given.
Arsenal had been unbeaten in home league action in 2023/24 before Thursday night and continued to probe and make chances, with Saka bringing an acrobatic save from Areola with a header.
An injury to Lucas Paqueta left West Ham without their talismanic Brazilian while the Gunners tried to walk in an equaliser. One opening saw Odegaard defer shot-taking responsibilities to Saka, then Gabriel Jesus and finally Gabriel Martinelli, who curled well wide.
Odegaard's inch-perfect pass slipped Saka in behind Angelo Ogbonna, leaving the 22-year-old bearing down on Areola. While his touch was inaccurate, Saka still struck the post before Trossard put the rebound wide.
Declan Rice nearly bagged what would have been a dream goal again his former side after receiving Trossard's pass, but the midfielder's strike from distance floated just over the bar.
Arsenal's profligacy in front of goal soon proved their downfall as one of their former players extended West Ham's lead. David Moyes' side once again struck with the home side in the ascendency, with Ward-Prowse's set-piece delivery proving crucial.
The former Southampton midfielder's corner was met powerfully by Mavropanos, whose brilliant header flew across the box into the opposite corner off the woodwork.
West Ham have been in remarkable form of late, picking up impressive wins against Spurs and Manchester United alongside heavy defeats to Fulham and Liverpool, but their stout defending could not be argued with as they inched their way towards all three points during the second half.
Saka's cross was tamely headed at Areola before the Brazilian ballooned another presentable opportunity in the air as Arsenal huffed and puffed unsuccessfully in search of a route back into the game.
Instead, it would be West Ham who were handed the best chance to score the match's third goal. Rice hacked down Emerson to gift his former side a penalty, but Raya enjoyed arguably his most confidence-boosting moment at Arsenal so far by beating away Said Benrahma's tame effort.
That was the last decisive action of the game, however, leaving Arsenal two points behind Liverpool at the top of the table. West Ham, meanwhile, move up to sixth.
Arsenal player ratings (4-3-3)
GK: David Raya - 7/10 - Was again quite an anxious presence in the Arsenal box but did at least enjoy a convincing moment late on with the penalty save,
RB: Ben White - 4/10 - Clipped in some dangerous crosses but rarely went on the outside in attack and was a little lightweight in defence.
CB: William Saliba - 5/10 - Was dragged out wide before West Ham opened the scoring. Struggled with Bowen's power.
CB: Gabriel Magalhaes - 5/10 - Played his part in a mishap with Zinchenko and lacked decisiveness in one of his poorer games.
LB: Oleksandr Zinchenko - 4/10 - Surprisingly bad in possession given his renowned technical ability and also offered little muscle in defence.
CM: Martin Odegaard - 7/10 - One of Arsenal's brighter sparks, constantly demanding the ball and giving his all in a doomed attempt to get his side back into the game.
CM: Declan Rice - 6/10 - Was persistent and combative in the middle of the park but was outwitted at crucial moments, even if his late error wasn't punished by Benrahma.
CM: Leandro Trossard - 5/10 - Played in a deeper midfield role but still got five shots away. Failed to make the most of his opportunities.
RW: Bukayo Saka - 6/10 - Struck the post and showed no signs of shirking responsibility with nine shots taken, though five of those were blocked.
ST: Gabriel Jesus - 4/10 - Offers plenty in Arsenal's build-up but a steelier edge in front of goal was needed for Arteta's side on Thursday night.
LW: Gabriel Martinelli - 5/10 - A quiet game and couldn't cause Coufal enough grief before coming off after the hour.
Substitutes
SUB: Eddie Nketiah (64' for Martinelli) - 6/10
SUB: Reiss Nelson (64' for Zinchenko) - 5/10
SUB: Emile Smith Rowe (79' for Trossard) - 5/10
Subs not used: Aaron Ramsdale, Cedric Soares, Jakub Kiwior, Jorginho, Mohamed Elneny, Ethan Nwaneri.
Manager
Mikel Arteta - 4/10 - Arsenal kept battering West Ham but the cool head to convert didn't show up, while Arteta's changes from the bench couldn't inspire any sort of comeback.
West Ham United player ratings (4-2-3-1)
GK: Alphonse Areola - 7/10 - Made eight saves in total in a solid display, commanding his box well even if his shot-stopping was flimsy-looking at times.
RB: Vladimir Coufal - 7/10 - Strong and robust out wide, seeing off the challenge of Martinelli well. Made five headed clearances.
CB: Konstantinos Mavropanos - 8/10 - Flicked in brilliantly to double West Ham's lead and was on hand to clear danger whenever necessary.
CB: Angelo Ogbonna - 7/10 - Complemented Mavropanos' assured display by leading the defence and repelling crosses.
LB: Emerson Palmieri - 7/10 - His cross caused the scramble that led to Soucek's goal, while his endeavour gave Benrahma the chance to make it 3-0, though that opportunity was wasted.
CM: Edson Alvarez - 7/10 - A tower of strength in the middle of the park, making five tackles.
CM: Tomas Soucek - 7/10 - Got into the box to pounce on the loose ball and score and also did his bit in the defensive third.
RW: Mohammed Kudus - 7/10 - Won the ball back nine times for West Ham in a great defensive showing, though didn't get many chances to show his talent in the final third.
AM: James Ward-Prowse - 7/10 - Wicked delivery from wide areas proved crucial as he assisted Mavropanos' header.
LW: Lucas Paqueta - 6/10 - Had some fleeting involvements before a suspected hamstring injury brought his evening to a premature end.
ST: Jarrod Bowen - 7/10 - Showed great ingenuity to set up Soucek's opener and didn't give Arsenal's centre-backs any time to rest or settle.
Substitutes
SUB: Said Benrahma (33' for Paqueta) - 5/10 - Missed the penalty late on which would have really sweetened West Ham's victory.
Subs not used: Lukasz Fabianski, Ben Johnson, Aaron Cresswell, Pablo Fornals, Maxwel Cornet, Danny Ings, Thilo Kehrer, Divin Mubama.
Manager
David Moyes - 9/10 - Questions are constantly asked over Moyes' future with his West Ham contract up at the end of the season, but with recent wins over Tottenham, Man Utd and now Arsenal, he's due some respite from all that unwanted attention.
