It was a harsh scoreline on the visitors, who were competitive for much of the game. Despite the loss, Molde are second in the group, with three games to go.
Arsenal, who spurned a couple of early chances, were left to rue their misses when they conceded in the 21st minute as Molde scored with their first shot of the game. Martin Ellingsen curled a delicious in-swinging shot into the bottom corner with his wand of a left foot.
The Gunners struggled to create opportunities for the rest of the half but were handed a lifeline when Kristoffer Haugen turned Eddie Nketiah's cross from the right into his own net just moments before the break.
Yet another own goal bailed out Arsenal when substitute Sheriff Sinyan bundled the ball into his own net from Joe Willock's cross at the hour mark.
Arsenal then made the game safe in the 69th minute when Nicolas Pepe guided Bukayo Saka's cross from the left into the bottom corner. Joe Willock grabbed a much-deserved goal in the 88th minute with a barn-storming finish to add further gloss on the scoreline.
On that note, here are the five major talking points from the game:
#5 Molde's opener shows the value of playing out from the back for Arsenal
Mikel Arteta's Arsenal have become well known for playing out from the back, despite the inherent risks involved. It's a tactic that has confounded old-school, traditional pundits, who are of the opinion that when in doubt, it's best to hoof the ball up the field.
Well, Martin Ellingsen's wonderfully-taken goal proved exactly why Arteta persists with his tactics. The percentages prove that an aimless kick out ends with the ball returning swiftly, leaving defenders out of shape. It's exactly what happened after Leno's goal kick was recycled by Molde with interest.
Arsenal do take a risk when they pass out from the back, with Leno conceding against Rapid Wien in that manner. However, the Gunners top the list for goals that have involved the goalkeeper in the buildup in the Premier League. So, perhaps there could be some merit in that strategy.
#4 VAR was conspicuous by its absence
For all the criticism that VAR has faced in the last couple of seasons, when it is unavailable, its absence is felt quite strongly.
Arsenal ought to have had a goal in the first half after Eddie Nketiah turned in Nicolas Pepe's cross when the Gunners were 1-0 down. Joe Willock's presence did not obstruct the goalkeeper's view, so it was a legitimate goal, yet the linesman had his flag up immediately. However, there was no VAR to overturn the goal.
VAR is absent in the group stage of the UEFA Europa League for simple economic reasons - the likes of Dundalk are unable to afford the high frame-rate, high-definition cameras that VAR requires. Yet, one can't help but hope that the sooner all of football has the technology, the better it would be.