Harvey Elliott featured for Fulham at 15 years of age as they won 3-1 at Carabao Cup opponents Millwall.
Joe Bryan, a £6m signing from Bristol City in August, opened the scoring with a low arrowed finish at the Den.
United States midfielder Luca de la Torre doubled the lead before Tom Elliott's header gave the hosts hope.
Cyrus Christie's 25-yard finish sealed victory before Elliott, aged 15 years and 174 days, came on as a substitute.
The England Under-15 midfielder, who is too young to sign a professional contract, trained with Fulham on their recent trip to Spain during the international break.