United were outplayed and outpaced in their worst performance of the season as Spurs ripped the hosts apart.
Spurs took the lead on three minutes as Micky van de Ven outstripped United's defence before crossing for Brennan Johnson to drive home at the far post.
For the next 25 minutes, Tottenham dominated with only Andre Onana in United's goal standing between them and a cricket score.
On 42 minutes, things turned worse for United when captain Bruno Fernandes was sent off for a late challenge on James Maddison. Fernandes slipped before catching Maddison and was shown a straight red by ref Chris Kavanaugh.
United were hoping to reset after halftime, but again fell further behind early in the second-half as Dejan Kulusevski converted a deflected cross from Johnson after a long run.
By this time, it was clear Spurs would be taking home the points and the result was confirmed with a third goal as Dominic Solanke stabbed home a flick from Pape Sarr from a corner on 77 minutes.
The result sees Spurs move into eighth position on the table, with United now sitting 12th.