City's comfortable 3-1 win at the Etihad Stadium reaffirmed the chasm between the teams and moved Pep Guardiola's Premier League leaders 12 points clear of United, who are languishing in eighth with a negative goal difference.
And former Premier League midfielder Craig Burley believes Manchester United chiefs should be alarmed by Mourinho's comments.
"We spoke at half-time that we could play better and we were much better with the goal from Aguero after five minutes of the half".
Manchester United finished in second spot in the Premier League last term after the Red Devils ended their first season under Mourinho in sixth place.
"If the third goal is scored in one of the moments where they were dominating I would probably say so but it comes in a moment where we were in the fight to get the equaliser", he said.
"We always pass the ball and try to find players between the lines in the best position possible to attack the opponent", he said.
"We need to look at what we have ahead of us and that is more important than looking at someone else". The card forced the Seagulls to try to weather the final hour down a man, which they nearly did ... until Sol Bamba scored in the 90th, denying Brighton what could be a vital point come the end of the season.More news: Bryce Harper Won't Be Signing With Yankees
To have a chance of overtaking City, Liverpool need a helping hand from other Premier League teams taking points off them but Van Dijk said that is not something which now bothers them. I can imagine when the result was 2-1 to bring on a fresh Fellaini, I think they would be in big, big trouble.
"When a goalkeeper makes a mistake, there is no one to save the goal".
That would mean United finishing behind City for a sixth straight season.
"Their next challenge is the European Cup because, until you win the Champions League, you can't really be compared to the best teams in Europe".
United's manager suggested recent matches at Bournemouth and Juventus had done his players no favours when City had faced Southampton and Shakhtar Donetsk at home.
"When he came to Manchester, you had to accept that he is going to play this kind of football". "Another three points, that's the most important thing, and a good performance from the whole team".