The Championship champions were swept aside by the Gunners who will unquestionably be title contenders once more.
Leeds boss Daniel Farke rightly pointed out that the game would not define their season and he would not analyse the game too much.
After their season opening victory against Everton, Leeds were brought down to earth by Mikel Arteta’s battle-hardened Premiership men who dominated from start to finish.
Farke said: “If you are not willing to suffer then we should have stayed in the Championship.
“We want to play in best league in the world so have to accept days like this can happen.
We stick together. I feel a bit for the players. The unity with our supporters - felt like it was just one of those days.”
After rolling out the welcome mat for their new £67.5m signing Eberichi Eze, who watched with the 60,110 crowd from the stands, Arsenal were quickly into their stride.
The blue-shirted visitors soaked up pressure and created their only meaningful effort on goal when Arsenal stopper David Raya tipped over a firm Pascal Struijk header from Anton Stach’s corner.
But it was in the opposing penalty area where the deadlock was broken via a familiar route – an Arsenal corner. On 34 minutes Declan Rice, outstanding throughout, sent the ball in for full-back Jurrien Timber to squeeze between Struijk and fellow centre-back Joe Rodon to head past Lucas Perri.
Up to that point United had defended well but the game was effectively over just before the interval when Ilia Gruev won possession but promptly gave the ball away. Within a flash Arsenal were able to release Bukaya Saka who smashed the ball past the static Perri.
Three minutes after the interval it became 3-0 when Viktor Gyokeres span in behind the Leeds defence, got round Struijk and drilled in his first Arsenal goal since his summer move from Sporting Lisbon.
Although they lost Saka and influential midfielder Martin Odegaard to injury, Arteta was still able to send on class replacements and saw his men stretch their lead with another pinpoint corner by Rice doing the damage. Once again Leeds could not deal with the delivery and Timber profited in the scramble by knocking in his second.
With 35 minutes remaining an absolute hammering was on the cards for Leeds who badly missed the midfield steel of injured skipper Ethan Ampadu who will be out of action for several weeks.
Farke sent on his replacements, including a first outing for new signing from AC Milan, Noah Okafor, but none of them could match the impact of Arsenal’s debutant whizz-kid Max Dowman.
The 15-year-old, who came of for Saka, saw plenty of the ball on the right wing, drew a booking from his marker Gabriel Gudmundsson before winning an injury-time penalty to allow Gyokeres to complete United’s misery from the spot.