Mohun Bagan squandered an early lead and went down 1-4 to their fancied hosts in their first match of the Under-15 Manchester United Premier Cup in Manchester on Tuesday.
The Kolkata colts took the lead through David Lalrinmuana, but their opponents quickly restored parity and the match was locked 1-1 at the end of the first 20 minutes.
The Indians were totally over-run in the second half as Manchester United struck thrice to seal victory.
Mohun Bagan face Sao Paulo FC, Brazil, later on Tuesday night and square off against Ferencvarosi TC (Hungary) and Athletic Club Bilbao (Spain) on Wednesday.