Centre-back William Saliba nodded Arsenal in front and Gabriel Jesus scored a header of his own in the first half before £34 million man Fabio Vieira struck a superb third, five minutes after the restart. Brentford had no answer as the visitors signed off before the international break with a fine win.
He could afford the luxury of bringing on teenager Ethan Nwaneri in injury time, with the 15-year-old becoming the Premier League's youngest-ever player.
Brentford, with England new-boy Ivan Toney in attack, made four changes of their own but they fell behind on 16 minutes when Saliba rose highest to nod in from a corner. After a brief delay while goal-line technology checked whether the ball had gone in, Saliba then celebrated his second goal of the season.
Brentford, who beat Arsenal 2-0 in their first ever Premier League match last season, were a world away from such a performance here, with Aaron Ramsdale totally untroubled.
The home side were finished off on 49 minutes when Vieira received Bukayo Saka's pass and sent a stunning drive past Raya to mark his first start in some style.
"We have a different mentality this season. we kept going and are training like we play and have class with the players that can make a difference," Xhaka told Sky Sports.
"You have the class in the front and they make the difference. More than happy we are in a good way but a long way to go."
Brentford boss Thomas Frank said: "We lost the game, I hate losing.
"They are top of the table so you cannot argue with that, they have done brilliant. Looking at the quality, they must be title contenders."
Arsenal face a north London derby showdown with third-place Tottenham once domestic football returns after the break, while Brentford are at Bournemouth.