Back at LCFC Training Ground after beating Crystal Palace 5-1 in Seagrave a week earlier, it was a difficult afternoon for the Foxes youngsters against a strong travelling Saints side.
Will Merry's 27th-minute goal saw the visitors ahead at the break, before captain Jem Hewlett headed Southampton into a two-goal lead. Kamari Doyle and Samuel Amo-Ameyaw then netted in quick succession to further increase the advantage early in the second half.
City did respond via Reece Evans, who converted Alfie Fisken’s cross prior to the hour mark, but both Doyle and Amo-Ameyaw soon added their second of the game to ensure it would be the south coast outfit who claimed all three points.
Leicester's Under-18s now sit 10th in U18 Premier League South, on seven points from seven games, ahead of hosting Blackburn Rovers Under-18s in their final U18 Premier League Cup group stage fixture (12:30pm GMT kick-off).
The details…
City: Addai, Grist (c), Joseph, Lewis (Nyoni 50'), McAlinney (Amartey 65'), Cook, Javaid (Toure 45'), Briggs, Evans, Fisken, Richards (Ononaye 45')
Unused sub: Weeks
Goal: Evans 58'