Neil Wood's side were down 2-0 in the first-half after two mistakes from returning loanee goalkeeper Matej Kovar.
The effervescent Hannibal Mejbri played his part in getting United back in the game by setting up Elanga to score United's first.
And the Red Devils had an equaliser on the stroke of half-time when Harvey Neville, son of club legend Phil, saw his teasing cross met by Elanga.
But Leicester retained their lead after another mistake from Kovar, whose indecisiveness saw him lobbed by Jacob Wakeling.
The Foxes then sealed their win through Thanawat Suengchitthawon.
Unfortunately for United, Elanga had to leave the game with a potential shoulder injury.