A three-goal burst either side of half-time was enough for a comfortable win that keeps us top of Group B.
Dundalk had come to defend in numbers and frustrate us - a tactic that looked to be working until Eddie Nketiah broke the deadlock late in the first half. The impressive Joe Willock doubled the lead moments later but the pick of the goals was Nicolas Pepe's right-footed effort in the first minute of the second half.
Debutant Alex Runarsson was called into action after just three minutes, making a full stretch low save from Patrick McEleney's 20-yard effort. The keeper would have been pleased to safely claim the resulting corner kick as well.
But from that moment on, the rest of the half was played almost exclusively in the visitors' half. The Dundalk rearguard were forced deep with Reiss Nelson and Pepe looking to provide the creativity from out wide.
Both had shots off target while Pepe also headed over from a Sead Kolasinac cross. Kolasinac had a header of his own tipped over, while Joe Willock's low drive was comfortably saved. Nketiah then missed with a snatched shot inside the six-yard box.
It was a case of attack v defence, with Dundalk's sheer weight of defensive numbers frustrating us.
Soon the pressure told though, and ultimately it was a mistake that led to the breakthrough. Visiting keeper Gary Rogers flapped at a corner and Nketiah was in the right place to sweep home.
Without a point to defend, Dundalk now had to change their approach, and were punished immediately. Willock smashed his shot into the roof of the net after Pepe's effort deflected into his path.
We had racked up 16 shots in the opening 45 minutes, and the half-time break provided only a temporary respite for Dundalk, with Pepe curling home a fine right-footed shot from the edge of the area just seconds after the restart.
Ainsley Maitland-Niles could have added a fourth but shot straight at the keeper as we kept our foot to the pedal in search of more goals.
Teenage striker Folarin Balogun was introduced for his debut in the final 20 minutes. The young American showed some nice touches in and around the box but was often crowded out by the Irish defence.
HOW IT HAPPENED
Mikel Arteta swept the changes, with only Granit Xhaka retaining his place from the defeat against Leicester at the weekend. He wore the captain's armband and lined up alongside Shkodran Mustafi – making his first start of the season – in central defence. There was also a debut for Icelandic goalkeeper Alex Runarsson, who joined the club in the close season.
WHAT IT MEANS
This was our first competitive match against an Irish side.
Alex Runarsson became the 875th different player to represent the Arsenal first team, and the first Icelander since Olafur Ingi Skulason in 2003.
Folarin Balogun became our 876th player, and our third American-born player after Frankie Simek and Danny Karbassiyoon.
We have scored in each of our past 18 European fixtures.
We had a total of 25 shots over the 90 minutes.
We conceded 20 fouls, Dundalk conceded zero.
It's a huge game on Sunday, against Manchester United at Old Trafford in the Premier League, while we're back in European action next Thursday – at home to Norwegian side Molde, who also have a 100 per cent record so far in Group B.
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