There were six changes to the team that lost to Arsenal in U18 Premier League South, with Harry French, Ryan Donnelly, Bobby Amartey, Kirsten Otchere, Bade Aluko and Jake Evans coming into the XI.
Reiss Russell-Denny opened the scoring for the hosts at Cobham Training Centre but Leicester roared back in the second half, with Jake Evans restoring parity just after the hour mark.
Less than a minute later, Toby Ononaye completed the turnaround, handing the visiting Foxes the lead.
That's how it stayed in the capital, with the side coached by Adam Barradell now awaiting who they will face in the last four of the competition.
Next up in the league, meanwhile, it's a trip to Tottenham Hotspur this Saturday (11:30am GMT kick-off).
The details
City: French; Aluko, McAlinney, Amartey, Joseph; Ononaye, Neale; J. Evans (King 85'), Donnelly (Khela 81'), Fisken (Dyke 71'); Otchere (Toure 85').
Sub not used: Bausor.
Goals: J. Evans 61', Ononaye 62'.