David Moyes masterminded his first-ever victory away to Arsenal as a manager as his unwavering West Ham United side ran out 2-0 winners against their London rivals at the Emirates Stadium.
The Scotsman had endured 22 triumph-less trips to the Gunners' turf prior to Thursday's Premier League affair, but a controversial Tomas Soucek opener and Dinos Mavropanos header against his old club saw the Irons subject Mikel Arteta's side to their first top-flight home loss of the new term.
Arsenal - who only avoided an even heavier defeat thanks to a David Raya penalty save from Said Benrahma - were not without their opportunities in North London, but a combination of alarming wastefulness, several sloppy passes and exemplary West Ham defending denied the Gunners the chance to rise back to the top of the Premier League table.
There was particular pre-match concern over Lucas Paqueta, who pulled up in the warm-up, but the Brazilian was cleared to start for West Ham, while Leandro Trossard deputised for the banned Kai Havertz for Arsenal.
Arteta's men unsurprisingly took the game to West Ham from the off, as Bukayo Saka shot straight at Alphonse Areola with three minutes gone, before Trossard fired over the top on the 11-minute mark.
Just two moments after Trossard's wasted chance, however, West Ham surged down the other end of the field and drew first blood against the run of play through Soucek, although his goal was shrouded in controversy.
An Emerson Palmieri cross from the left caused chaos, as Oleksandr Zinchenko and Gabriel Magalhaes got in each other's way and looked to have conceded a corner, but Jarrod Bowen kept the ball alive and cut back for Soucek to prod home.
The goal was given on the field, and as the VAR room could not definitively prove that the ball had stayed in or gone out of play due to a lack of suitable camera angles, the Irons' opener was ratified, akin to Anthony Gordon's contentious winner for Newcastle United against the Gunners last month.
Arsenal's attempts to respond were met with stiff resistance by a well-organised Hammers defensive unit, whose effective pressing was limiting the hosts to few clear-cut chances, although Areola had to make an acrobatic stop from a Saka header on the half-hour mark.
Mere seconds passed before Paqueta succumbed to the injury which appeared to plague him in the warm-up - Benrahma took his place - but West Ham survived one final scare to enter the break in the ascendancy, as Saka struck the post from close range in the 42nd minute before the rebound bounced off an unawares Trossard and out of play.
Normal service resumed after the interval, as Declan Rice tried his luck from distance in the 53rd minute and grazed the roof of the net, but while the former Hammer could not haunt his old team, an erstwhile Gunner compounded the hosts' misery moments later.
After Arsenal had wasted a succession of corners in the first half, set-piece master James Ward-Prowse sent in an inviting delivery in the 55th minute, and Mavropanos escaped Zinchenko before directing a header off the crossbar, off the inside of the post and into the net.
The Greek centre-back kept his celebrations to a minimum against his former employers, who had two golden chances to respond through a pair of Gabriel Jesus headers in the 65th and 66th minutes, but his first effort landed in Areola's arms before his second sailed over the top with half of the goal at his mercy.
Arteta's men tried in vain to up the ante towards the end, as Trossard, Saka, Emile Smith Rowe and Eddie Nketiah all sent tame efforts into the arms of Areola - still being offered incredible protection by his teammates - in the final 20 minutes.
The Frenchman was forced into a diving save from Odegaard's long-range strike in the 90th minute, and just when it appeared that Arsenal's evening could not get any worse, Rice slipped and tripped Emerson in the area to give away a last-minute penalty.
Benrahma - who scored from the spot at the Emirates in December 2022 - sought to repeat his feat from the 12-yard mark, but Raya sprung to his left and beat away the Algerian's penalty, thus sparing Arteta's men from further humiliation in front of a half-empty Emirates.
Arsenal - who stay two points below Liverpool in second - will try to respond when they meet another London rival in Fulham on New Year's Eve, while West Ham, now up to sixth, have a four-day rest period before they host Brighton & Hove Albion on January 2. body check tags ::
