They lasted all of 11 seconds before Christian Eriksen gave Spurs the lead, finishing emphatically past David de Gea after first Phil Jones, then Chris Smalling, failed to clear the ball. Eriksen's effort was lagging some way behind the world record of 2.1 seconds - step forward Gavin Stokes in a match between Maryhill Juniors and Clydebank past year - but it would be hard to think of another United game when their first touch of the ball has been to pick the ball out of their net.
Quite how rattled United were was fully realised when Jones stuck the ball into his own net some 27 minutes and 49.5sec after Spurs opened the scoring.
Mourinho revealed afterwards his players had watched videos of the way Mauricio Pochettino's side start games but admitted the planning had not paid off.
Stoke and Watford played to a stale goalless draw at the Bet 365 Arena, with neither side being able to separate themselves from one another despite chances falling at both ends of the scale.
Pep Guardiola's all-conquering City took their tally of goals in all competitions this season to 100 when the outstanding De Bruyne, who had provided a superb first-half assist for Fernandinho to shoot home, scored their second.
'It was a really, really bad goal. "A team to win matches needs to score goals and also defend well - on this occasion we were very bad".
"After that, we were in Tottenham's hands".
Mourinho went on to claim he was forced to replace Fellaini shortly after he was thrown into the action to the final third of the game, as he hinted the Belgian midfielder had an injury. "I wanted to change the structure and after a couple of minutes he was injured", he said.
Performance of the night came from Everton new boy Theo Walcott, who scored his first two goals since signing from Arsenal in the 2-1 victory over Leicester City. Christian Eriksen believed that it would arrive in this situation.
'We deserve a lot of praise but the most important thing now is to keep consistent'. We tell the young players to always anticipate. "It was massive to be up early in the game". "It is not easy to keep up this kind of performance because we are going to play every three or four days", the Argentine told reporters.