Unai Emery, the current manager of Arsenal claimed his first win in charge of Arsenal as Issa Diop's own goal and a stoppage-time Danny Welbeck strike secured a 3-1 Premier League victory over West Ham at Emirates Stadium.
Arnautovic asked constant questions of Arsenal's high and shaky backline and had already thrashed into the side netting before he exchanged passes with Felipe Anderson to arrow a 20-yard drive into the bottom corner.
Bellerin's mistakes at the other end remained a problem, with Sokratis Papastathopoulos forced into a desperate block from Felipe Anderson before the Spain full-back played Robert Snodgrass onside to shoot too close to Petr Cech.
Diop allowed Alexandre Lacazette too much room to turn and shoot, with ex-Arsenal goalkeeper Lukasz Fabianski beating the shot away, and the 21-year old centre-back was the architect of his own misery 20 minutes from time.