Gabriel Martinelli and Emile Smith Rowe struck in the second half to earn Arsenal a 2-0 win over West Ham at the Emirates Stadium to move the Gunners into the Premier League's top four.
Following a keenly contested first half in which Kieran Tierney struck the bar, Martinelli raced into the box in the 48th minute to slot a classy finish into the bottom corner.
The Gunners continued to assert their dominance in the second half as Alexandre Lacazette won a penalty, with Vladimir Coufal receiving a second yellow and a red for the challenge, but the France international's spot-kick was saved by former Arsenal goalkeeper Lukasz Fabianski.
However, substitute Smith Rowe lashed home late on to secure an important result that sees Arsenal leapfrog the Hammers into fourth place, one point clear of their London rivals after 17 games.
The Gunners went close before the interval, Tierney racing onto a loose ball and blasting towards the top-left corner, only for Fabianski to get the slightest of touches to turn it onto the crossbar.
Martinelli scored the decisive goal shortly after the restart, latching onto Lacazette's sublime throughball to curl firmly into the bottom-right corner.
Lacazette was involved again in the 66th minute as Coufal slid in to win the ball from him in the box, fouling the striker and being sent off for a second bookable offence, but the Arsenal forward's penalty was kept out in the bottom-right corner by Fabianski.
With only 10 men, West Ham were caught out as they pushed for an equaliser, with Smith Rowe coming off the bench to drive towards the edge of the box and steer a left-footed drive into the bottom-right corner to seal an important win.
10 - 10 of @Arsenal's 23 Premier League goals this season have been scored by players aged 21 or younger (Smith-Rowe x6, Martinelli x2, Saka x2), the most U21 goals for any team in the competition this campaign. Bright. pic.twitter.com/Qyh2DfQQTl— OptaJoe (@OptaJoe) December 15, 2021
What does it mean? Arsenal up to fourth
Arsenal's victory sees the Gunners move one point clear of West Ham and into fourth in the Premier League table, at least temporarily.
Manchester United are just two points behind in sixth, and have a game in hand on the north London side.
The boy from Brazil
Martinelli's winning strike was his seventh Premier League goal; the only Brazilian with more in the competition before their 21st birthday is Gabriel Jesus (16).
Gunners firing blanks from the spot
Arsenal have now failed to convert three consecutive penalties in the Premier League for the first time since August 1992, when they failed to score with each of their first five penalties in the competition.
Arsenal travel to face Leeds United at Elland Road on Saturday, while West Ham host struggling Norwich City on the same day.