Donald Love and Andreas Pereira gave United an early lead but we soon found our rhythm and pulled one back through Will Miller.
We kept plugging away in search of an equaliser and it duly arrived courtesy of Joe Pritchard with just a few minutes left.
But the visitors wouldn't be denied and Guillermo Varela's stoppage-time volley gave them all three points and sealed their second consecutive Barclays Under-21 Premier League title.
Spurs U21s: McGee, Walker-Peters, Lesniak, Walkes, Muscatt, Stylianides (Goddard 86), Winks, Onomah, Sonupe (Edwards 72), Miller (c, J Pritchard 67), Sterling. Substitutes (not used): Marsh, Glover (GK).
Manchester United U21s: J Pereira (c), Varela, Tuanzebe, Williams, Borthwick-Jackson, McNair, El-Fitouri, Love, Redmond (McTominay 62), A Pereira, Riley. Substitutes (not used): Poole, Mitchell, Reid, Henderson (GK).