Ugo Ehiogu's players performed admirably against a United side fielding six players with first team experience this season.
Trailing 2-0 early on, they almost kept United's champagne on ice as goals from Will Miller and Joe Pritchard levelled it up.
However, with less than a minute remaining of four minutes added time, Guillermo Varela - 11 first team appearances for United this term - pinged a volley into the top corner. That goal puts United in an unassailable position at the head of the table.
A point would have taken us up to fifth tonight but the team will have to wait for their final position with teams around us yet to complete their programmes.
Luke McGee returned in goal for Spurs with Josh Onomah and Harry Winks also starting and there was zip about the lads' performance all night with some lovely patterns of play.
With the title up for grabs, United shot into an early lead. Paddy McNair found Andreas Pereira who laid off for Donald Love, timing his run to perfection to drill low past McGee.
We'd started with purpose though with Onomah and Winks buzzing around and got into a number of decent positions wide with no reward.
It therefore came as a bit of a body blow when United struck again with only their second effort on target. It was another clinical finish as this time Varela clipped in for Andreas Pereira to volley home on the full from 12 yards for 2-0, 16 minutes on the clock.
Undetered, we continued to chip away, crisp, short passing in and around a United side that were now happy to sit in and try to break.
We had a sighter when Miller's cross was cleared to Winks, who fired wide on 21 minutes but five minutes later, we reduced the deficit.
The ball went through a number of players this time before Zenon Stylianides picked out Miller on the edge of the box. He looked penned in but managed to shift the ball out of his body and drill low across Joel Pereira into the bottom corner.
We were on top now and came close to levelling before the break. Cameron Borthwick-Jackson's cross landed at Winks' feet again and this time, the midfielder found the target, forcing Joel Pereira to touch wide at full stretch. Filip Lesniak then hit a dipper just wide from 30 yards.
Miller was back in the action at the start of the second half as Onomah got away from Axel Tuanzebe left side before prodding the ball to Miller, who found Joel Pereira in the way at the near post.
However, United, quiet in attack since their second goal, had the next two chances. The first came from nothing as McGee's pass out from the back went straight to Love, who missed the target from the edge of the box. Minutes later, Andreas Pereira darted into the box only to shoot wide.
We were straight back up the other end as Winks shot just over before Anton Walkes attempted an ambitious volley, teeing the ball up for himself before hitting a dipper onto the roof of the net. McGee then did well to clutch substitute Scott McTominay's near-post flick on the line.
The next chance arrived in the 80th minute as United broke quickly from our attack, Andreas Pereira got away from Walkes, sprinted to the box and curled onto the post from 16 yards.
Winks and Stylianides opened it up for Onomah to shoot straight at Joel Pereira before we finally found a way through with six minutes remaining.
It was all about our late substitutes as Stylianides played in Marcus Edwards right side and his low cross was dispatched impressively by Pritchard - his second goal against United this season.
The chances kept coming. McGee got down well to take Borthwick-Jasckson's low shot, Edwards was denied by Joel Pereira from the right angle and Joe Muscatt was inches away from Onomah's cross.
It looked for all the world that if there was to be a winner, it would be us, but United turned it upside down in the final minute. Onomah did well initially to block McTominay's shot on the line but the ball came out to Varela, who hit an unstoppable shot into the top corner.
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).