After 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.