Sadly, Spurs only really showed what they can do in the first half, when they were the better team overall. They attacked United, passed the ball well, and created several great chances and made United look ordinary and very beatable, especially in the first 25 minutes or so. United's first goal came about (like so many Spurs concede) due to a defensive error (this time by Dembele, who is usually better than that) that gifted United the ball in a dangerous position. But apart from that, Spurs didn't really look troubled. Both sides played well, but Spurs created the better and greater number of first half chances.
However, in the second half all of Tottenham's recent failings came back to haunt them. Their previous attacking drive disappeared, they reverted to possession-football, with all the side-to-side, pass to backwards, side-to-side, pass it backwards bollocks which is simply infuriating to watch, not least because, unsurprisingly, it creates precious few chances. I know Pochettino's style of play has yielded success, but it's often not pretty to watch, and if the opposition sits back and defends (which United largely did, albeit with some decent counter-attacking breaks which were mostly squandered), it can be very difficult to break through unless someone breaks cover and moves the ball forward quickly and crosses it into the box occasionally.
I love Spurs, but we got exactly what we deserved based on our second half performance, which was lacklustre. And until the players can find it within themselves to attack throughout an entire game, when they are not only far more threatening and likely to score, but also concede very few, then they risk coming undone in games like this where the opposition possesses quality players that can defend and counter.