Duncan Watmore scored the only goal of the game for the Black Cats in the 48th minute, racing onto George Honeyman's pass and firing across Luke McGee from 18 yards.
Sunderland goalkeeper Jordan Pickford denied Josh Onomah and Shayon Harrison planted a one-on-one chance just wide as we pushed for an equaliser in the second half.
Spurs U21s: McGee, Walker-Peters, Ogilvie, Lesniak (McEneff 74), Veljkovic (Stylianides 74), Maghoma, Miller (McEvoy 59), Winks, Harrison, Onomah, Oduwa. Substitute (not used): Miles (GK).
Sunderland U21s: Pickford, J Robson, T Robson, Agnew (c), Cartwright, Beadling, Gooch, Smith, Mandron (Greenwood 85), Honeyman, Watmore. Substitutes (not used): Nelson, Casey, Blinco, Burke (GK).
Below: Josh Onomah's effort blocked by Thomas Beadling in the first half