A Christian Fuchs own goal and a last-gasp Eddie Nketiah tap-in saw the visitors secure a 2-0 victory – leaving them with a trip to either Lincoln or Liverpool next week.
This was the only third-round clash between two Premier League sides but neither really resembled their strongest XI with both Jamie Vardy and Pierre-Emerick Aubameyang given the night off.
✅ Progression secured!
🏆 #CarabaoCup— Arsenal (@Arsenal) September 23, 2020
Arsenal boss Mikel Arteta made seven changes as weekend match-winner Nketiah was recalled alongside the likes of David Luiz, Mohamed Elneny and Nicolas Pepe.
Despite the rotation, there was no room in the matchday squad for either Mesut Ozil or Matteo Guendouzi – who are yet to kick a ball for the Gunners this season.
Brendan Rodgers named a completely new Leicester XI to the side that beat Burnley on Sunday as James Maddison was handed his first start of the campaign.
Reiss Nelson, recently linked with a loan move away from Arsenal, started well and came close to an opener, forcing a fine save out of Danny Ward in the Leicester goal.
At the other end, Bernd Leno kept his spot despite the signing of Iceland international Alex Runarsson and he, too, did well to prevent Kelechi Iheanacho putting the hosts in front.
Arsenal then enjoyed a period of dominance, Pepe should have done better when picked out inside the box but tried to cut back instead of shooting and the danger was cleared.
Nelson then passed up a glorious chance of his own as he shot well wide when in a good position, while Bukayo Saka saw a strong penalty claim turned down after being felled by Daniel Amartey.
Rodgers’ side finally started to whir into life as the half wore on and Maddison was unlucky to see a curling effort hit the post.
The second half started slowly as torrential rain began to fall over the King Power Stadium as Arsenal took the lead in fortuitous circumstances.
Pepe had been largely ineffectual but he did well to squeeze in a cross that hit the post and ricocheted off Fuchs and into his own goal.
Nketiah, sent off when these sides met in the league towards the end of last season, came close to settling the tie as he lobbed the ball towards goal only for Wes Morgan to race back and head clear off the line.
The Foxes turned to Dennis Praet and Ayoze Perez off the bench and the latter had a shot blocked soon after his introduction.
But the former Newcastle forward should have levelled with 10 minutes to go, sending a free header wide from close range – much to the chagrin of Rodgers on the touchline.
Nketiah would then secure the result, bundling over from almost on the line in stoppage time.
If Liverpool beat Lincoln on Thursday it would see Arsenal make two trips to Anfield next week, with the fourth-round tie following on from a Premier League meeting on Monday night.
