These two teams have experienced frustratingly inconsistent seasons, highlighted by their unreliable backlines. The error-strewn performances in north London left both sets of supporters despairing and roaring during a rollercoaster contest.
Fraser Forster twice fumbled with the ball at his feet for United goals, allowing Ruben Amorim's side to come back from 3-0 down to 3-2. But, with the visitors piling forwards and threatening an equaliser as tension ramped up in Tottenham, Altay Bayindir allowed a Heung-Min Son corner to go in over his head.
Add that to his poor parry out for Dominic Solanke to open the scoring on the night and it is hard to judge which stand-in stopper had the worse performance - but they were not alone.
' Gary Neville slammed Lisandro Martinez for his "wimpish" flick to Dejan Kulusevski for Spurs' second goal, which came just 46 seconds into the second half. The home side scythed through the United defence again soon after, with Solanke stepping inside Martinez before shooting through the legs of Jonny Evans to seemingly put Spurs in cruise control.
TrendingIt is rarely that straightforward for Spurs, though, and Forster's poor pass in his own box was pounced on by Bruno Fernandes for Joshua Zirkzee to tap in before the 'keeper was chased down by Amad Diallo for the second. Even deep into stoppage time Spurs found capacity to concede from a set-piece, with Evans nodding in to ensure the final seconds were as chaotic as what had come before.
There were huge cheers from the home fans when that final whistle did come. Their hopes of ending their trophy drought have been boosted - although if their final-four clashes with Liverpool, who they were drawn against after the game, are as wild as this it is impossible to call whether they will make it to Wembley or not.
Man Utd's momentum after their Manchester derby win, meanwhile, has stalled. From the off-field issues around the future of Marcus Rashford to the on-field problems, Amorim has a big task on his hands - although both he and Ange Postecoglou will hope their sides can deliver more consistent and controlled success in the future when their long list of absentees return.
Tottenham boss Ange Postecoglou on :
"We made it harder than it should have been, we were well in control, played really well, we looked like we were going to manage the game and then two unfortunate moments, the first one affected Fraser and then the second one came as a result of that. But we showed character and scored a fourth.
"I like the whole game. Are you not entertained? I know the studio is probably having a meltdown over my lack of tactics.
"We've got so many absences at the moment, centre-halves, kids on the bench. If we get through this period we're going to get enormous growth out of it."
Man Utd boss Ruben Amorim:
"We controlled the possession. We were not the best team in all of the game but in most of the parts I think we were the best team. We disconnected for eight minutes and it was hard to recover from that, but the lads did a great job to recover. We were so near the draw but the fourth goal was really hard for us.
"We disconnected for eight minutes and that cost us the game."
On whether the decision to omit Rashford again was a mistake: "If I feel I do the right thing for the team, it was never a mistake. We have to make a selection. It was not a mistake because I feel I'm doing the best for the team in my way of seeing things."
Jamie Redknapp:
"If it was not so serious, it would be hilarious! But it was a masterclass on how not to see a game out from Tottenham. It was crazy to see, but a big result for Spurs which gets them into the semi-finals - but how often do we see it from them?
"I do not know how the manager does it at times, he must be pulling his hair out, but some of the things are his fault, like passing the ball back to the goalkeeper - Forster is the worst player on the pitch with the ball, so stop giving it to him.
"Absolute madness at times, but the chaos was so enjoyable."
Gary Neville:
"Spurs just about deserved to win in the end, but what a strange game of football, mistakes galore, goalkeepers all over the place and Spurs come through in the end.
"You felt arriving this evening it was a big night for Postecoglou and Spurs and maybe that just got them over the line in the end."
Jamie Carragher:
"Because of how Spurs have been at times this season, throwing away leads, you just felt the shift in momentum around the stadium.
"Everyone was feeling the same thing when Man Utd scored their first goal, it was just when are United going to get the second.
"What I will say is Spurs are the most entertaining side in this league and every time I want them, it is a great game and they have had another absolute belter here."