Runar Runarsson made his debut in the Arsenal goal following his arrival from Ligue 1 side Dijon FC, with Willian, Pierre-Emerick Aubameyang and Alexandre Lacazette named on the bench.
Arsenal gave the Irish side no room to breathe in the opening minutes with a pressing move from the left presenting Reiss Nelson an opening, but he dragged wide of the near corner.
A bright spell from the Gunners in the final ten minutes of the half found Joe Willock going out wide to play in Sead Kolasinac at the far post, but Gary Rogers pushed the Bosnian's header over.
The Gunners deservedly grabbed the lead 42 minutes in when Eddie Nketiah reacted smartly to a loose ball from Rogers following a corner-kick to stab into an empty net.
Arsenal made it two goals in two minutes as a sweeping move found Willock in an open space on the far side of the area before arrowing into the roof of the net.
The visitors freshened up their stall at the start of the second half, with Sean Murray pulled off for Greg Sloggett.
However, Arsenal continued their scoring act 30 seconds into the second period when Nicolas Pepe retrieved a ball from the right-side for a fabulous finish into the top corner.
Mikel Arteta's side weren't satisfied and gunned for more goals in the final quarter through Willock, Nketiah and Ainsley Maitland-Niles, but Rogers managed to pull off a few saves.
Dundalk targeted a consolation from a counter-attack towards full-time, while the Gunners maintained momentum for a resounding victory.