After 11 minutes Raphinha was beaten far too easily down the right and nobody thought to get close to former Leeds loanee Nketiah before Gabriel Martinelli's pull-back picked him out to score the second.
Then, after 28 minutes, Leeds's captain for the day Ayling launched into a brainless two-footed tackle on the Brazilian, making contact behind the byline. Chris Kavanagh somehow thought it was only worth a yellow card until video assistant referee John Brooks suggested he go and have another look on the pitchside monitor.
Ayling was not just shown a red card but is now set to have his season ended by suspension.
Forget the fact that Everton were leading, dropping Leeds into the bottom three, the visitors were an absolute mess.
They showed some belated fight in the second 45 minutes but you can try as hard as you like - play football as bad as they did in the first period and you will not pick up Premier League points.
Scoring from their first of only two efforts on target gave the scoreline some respectability, salvaged a modicum of pride and sent a few Arsenal butterflies fluttering but it could not diguise just how badly they had let themselves down before the break.
Leeds preferred Premier League debutant Lewis Bate to Klich and took their most talented player, Raphinha, when they needed a couple of goals to salvage a point - February's spectacular capitulation means goal difference is irrelevant to them. It was not a decision you could argue with at all given the feebleness of his performance.
They had been indisciplined from the start, Junior Firpo - now their only full-back for the final three matches of the season - conceding a free-kick for shoving Bukayo Saka over after just 98 seconds.
Raphinha was booked for dissent - quite what his argument was would be fascinating to know - as Kavanagh came across to upgrade Ayling's card, and Mateusz Klich was cautioned for a tackle from behind on Granit Xhaka.
On top of the red card and the suspension came a triple whammy - Joe Gelhardt was substituted half-an-hour into his first start since Arsenal came to Elland Road before Christmas, pushing Dan James back into the lone centre-forward position he had finally escaped.
Other jobs he would take on during the game included right winger, messenger boy when Marsch wanted a note passing to Kalvin Phillips, draft excluder at a free-kick Odegaard floated gently into the hands of Meslier and sweeper as Arsenal tried to break away from a 90th-minute corner Leeds had rightly sent Meslier up to attack.
There are lies, damned lies and statistics but one half-time number told the story fairly accurately: Arsenal 11 shots, Leeds nil.
Meslier - for whom every backpass now seemed like an act of cruelty by his team-mates - saved from Martin Odegaard after 23 minutes and saw a Saka shot thump into his chest very soon after.
Another Firpo foul on Saka just the right side of the area from a Leeds perspective saw Meslier get a hand to Odegarrd's spinning shot but not a strong enough one that Diego Llorente did not have to keep it out of the goal.
The second half was a show of defiance from the terraces, those who had not brought scarves twirling the T-shirts wishing Stuart Dallas the best above their heads. Like the players, the club had dealt in half-measures, not supplying enough for everyone.
The half-time break seemed to have focused on-field minds a bit even if it could not change the fact they had fewer players against a better, more confident team. It also seemed to take the sting out of Arsenal who played even more of the game around Leeds's final third, but with none of the previous intensity.
Meslier saved from Martinelli after the winger put Raphinha on his backside but plentiful possession amounted to very little and when Firpo flicked on a corner for Llorente to tap in, the nerves started.
"Forwards! Forwards!" came increasingly desperate cries from the supporters around the press box.
Rodrigo headed a free-kick at Aaron Ramsdale in the fourth added minute but for Leeds to have got anything out of a game they were so awful in for 45 minutes would have been just plain wrong. Now they have to make keep the after-effects of that half to a minimum.
Arsenal: Ramsdale; Cedric, Holding, Gabriel, Tomiyasu; Elneny, Xhaka; Saka (Pepe 68), Odegaard, Martinelli (Smith Rowe 78); Nketiah (Lacazette 90).
Unused substitutes: Leno, Tavares, Lokonga, Oulad M'hand, Swanson, Patino.
Leeds United: Meslier; Ayling, Llorente, Koch, Firpo; Klich (Bate 46), Phillips; Raphinha (Rodrgio 60), Harrison; James, Gelhardt (Struijk 29).
Unused substitutes: Klaesson, Hjelde, Cresswell, Greenwood, Shackleton, Gray.
Referee: C Kavanagh (Manchester).