The deciding goal was scored by Leicester’s Kian Pennant with 20 minutes to go. He took advantage of some hesitation to collect possession out on the left and he finished off a solo effort with a strong run and left-foot shot low past Prince Adegoke.
In retaliation, Stutter had a near-post shot saved and Mothersille put another Chelsea chance over but an equaliser proved elusive.
The defeat means Chelsea drop to second in the U18 Premier League South table, one point behind Crystal Palace. Next up it is back to Cobham next weekend for a match against eighth-place West Ham.
Chelsea Prince Adegoke; Richard Olise, Josh Tobin (c), Brodi Hughes, Luke Badley-Morgan (Derrick Abu 76), Billy Gee, Samuel Rak-Sakyi (Alfie Gilchrist 61), Silko Thomas (Edwin Andersson 76), Leo Castledine, Malik Mothersille, Ronnie Stutter.