Mourinho said he left Stamford Bridge with a "very good feeling" but will not let the reception of the home fans get in the way of the quest for another three points.
"I have to try and forget it and do my job as I go there as Man United manager now.
"I knew that working in England and the Premier League I would, sooner or later, have to play against Chelsea and go to Stamford Bridge and the computer has decided that I go now.
"I will always have an amazing affinity with Chelsea and their fans, so we have good memories together, but tomorrow my focus is on winning another important game for Man United.
"My feeling is that it will be tight, very close for the title and probably one team who are challenging for the title in March doesn't finish in the top four so I think it is going to be really tight."
Antonio Conte's side suffered back-to-back defeats to fellow contenders Liverpool and Arsenal in September but have since steered their season back on track with successive victories over Hull and champions Leicester last time out (having also knocked the Foxes out of the League Cup).
This match is the third of three in six days with Wednesday's cup derby with City on the horizon and United go to West London unbeaten in six and five points behind Guardiola's early league pacesetters.
Chris Smalling picked up a minor muscular injury in Thursday's win over Fenerbahce but is expected to be fit to play while Henrikh Mkhitaryan will soon be ready for a comeback.
The Armenian has not featured for us since the derby defeat on 10 September but returned to training this week and could be available.
Antonio Valencia, Ander Herrera, Zlatan Ibrahimovic and Marcus Rashford all sat out the 4-1 win over Fenerbahce and look set to be recalled while Cesc Fabregas, Kurt Zouma and Branislav Ivanovic again miss out for Chelsea.
Form guide: Chelsea D L W L W W United W W W D D W
Match odds: Chelsea 6/5 Draw 11/5 United 12/5
Referee: Martin Atkinson