Andre Onana's howler seals defeat for United at home as struggling Spurs suffer another defeat at Everton in Premier League football.
Manchester United's season has become even more turbulent after a 3-1 home defeat to Brighton in the Premier League.
United suffered a miserable defeat after goals from Yankuba Minteh, Kaoru Mitoma and Georginio Rutter at Old Trafford on Sunday consigned United to their 10th league defeat.
Bruno Fernandes scored for United from the penalty spot, but the hosts were not helped by a howler from goalkeeper Andre Onana, who played a routine pass from a low cross into the box, allowing Rutter to tap in the loose ball.
It was the seventh defeat in 15 games in total under new coach Ruben Amorim and highlighted the enormous job the Portuguese coach has on his hands to revive the 20-time English champions.
Brighton moved up to ninth place with 34 points, four points off the top four. United are in 13th place with 26, also in 22 games.
Brighton have won six of their last seven league games with United and their last three visits to Old Trafford.
The teams were led with bagpipes in memory of the great Denis Law, who passed away this week, and former manager Alex Ferguson laid a wreath in the center circle.
Brighton took the lead after five minutes when Mitoma beat the offside trap on the left following a long ball from Carlos Baleba and his cross-field pass provided an easy finish for an unmarked Minteh.
United won a penalty midway through the first half when Brighton attempted to play the ball out of defence, but goalkeeper Bart Verbruggen's pass was poor and the ball fell to Joshua Zirkzee in the area.
Baleba put his arm on the shoulder of the forward, who went to the ground. Referee Peter Bankes pointed to the spot and Fernandes had no problem tying the score.
Brighton thought they were back in front seven minutes into the second half when United failed to clear a low free kick inside the area and Pedro fired home. But a VAR check ruled that Jan Paul van Hecke had kicked Diogo Dalot's foot in the melee.
However, the visitors got a second on the hour when Mitoma stretched at the far post past United defender Noussair Mazraoui to convert an inviting Minteh cross.
Brighton then scored a third thanks to Onana's horrendous error to clinch the game and leave United contemplating their 10th league defeat.
Elsewhere, Tottenham Hotspur's woeful campaign also sank to new depths with a 3-2 loss to relegation-fighting Everton. But Nottingham Forest's unlikely title challenge is going from strength to strength after a 3-2 win against bottom-placed Southampton.
