Christian Fuchs misjudged the bounce of a ball to free Bukayo Saka, who released Pepe in the area. Pepe’s initial cross was blocked by goalkeeper Danny Ward, but then his shot on the rebound came back off a post and took a wicked deflection off Fuchs to fly into the unguarded net.
It was a goal that had been coming, and it was the first own goal Arsenal had benefited from since April 2019.
Leicester did have a chance to equalise in the 81st minute, arguably against the run of play, but substitute Ayoze Perez headed Marc Albrighton’s free-kick wide of the near post.
Arsenal completed a routine win in added time when Nketiah poked the ball past Ward, as the Leicester goalkeeper and defence hesitated.
In cup competitions, Arteta seems to have the magic touch.
Leicester City (3-4-3): Ward 5; Amartey 6, Morgan 6, Fuchs 5; Albrighton 5, Choudhury 5, Dewsbury-Hall 6 (Perez 76), Thomas 6; Gray 6, Iheanacho 5, Maddison 6 (Praet 72).
Subs not used: Jakupovic (g), Justin, Tielemans, Barnes, Knight.
Arsenal (3-4-3) Leno 6; Holding 6, Luiz 7, Kolasinac 7; Maitland-Niles 6, Willock 6 (Ceballos 78), Elneny 6, Saka 6 (Bellerin 87); Pepe 6, Nketiah 6, Nelson 7 (Willian 72).
Subs not used: Runarsson (g), Bellerin, Saliba, Lacazette, Xhaka.
Referee: Peter Bankes (Wirral).