United players entered the dressing room 4-1 down, furious at their own performance and enraged by the manner in which Anthony Martial had been sent off.
Martial had been given his marching orders after being provoked by Erik Lamela and petulantly slapping him.
Lamela had made the most of it, falling to the floor and clutching his face, and United’s players were furious with the Argentina winger.
And Mourinho’s decision to hook him off at half-time was viewed as a ‘masterstroke’ by the United dressing room.
A source told The Athletic: ‘The players thought he was a disgrace.
‘At half-time, the United players all knew Lamela had faked it.
‘They were angry. Jose did a masterstroke to take him out.’
The result left United in 16th place after three matches, with their sole win coming – somewhat fortuitously – against Brighton.
United will return to action after the international break against Newcastle, while Spurs welcome West Ham.