United scored twice in the second half through Bryan Mbeumo and Patrick Dorgu, and they also had three goals ruled out for offside, hit the woodwork twice and forced visiting goalkeeper Gianluigi Donnarumma into a string of saves.
The hosts could have been reduced to 10 men inside the first 10 minutes when full-back Dalot caught Jeremy Doku in a knee-high challenge with his studs.
Referee Anthony Taylor brandished a yellow card for the Portuguese and the decision was supported by the video assistant referee (VAR).
The Premier League match centre explained the decision by saying: “The referee’s call of yellow card to Dalot for a reckless challenge was checked and confirmed by VAR – with the contact deemed to be glancing and not with excessive force.”
Guardiola said: “It’s a red card but it would be poor as a manager to analyse that as the reason for [losing] the game – it is what it is.
“For 85 minutes 10 against 11 I believe, but if we played with the energy that we did, we were nowhere near that. I could say that and blame [the decision], but we will not grow up and move forward.
“It happened and it is not a surprise, it happened in the past when I arrived here. Honestly, we have to look at ourselves. If the players have excuses, we will be in trouble in the future.
“We have to look at ourselves and today the analysis is simple – Manchester United were better and we have to accept it.”
Former Premier League official Darren Cann told BBC Sport he thought Dalot was “very fortunate to escape a red card”.
“It’s a hard one to see at normal speed live on the pitch from the referee’s angle but with the benefit of replays I do feel that Dalot is very fortunate not receive a red card,” he added.
“Had the referee been invited to the screen I am sure he would have been shown a red card.”
Interim United boss Carrick said: “I am not giving you that [Guardiola’s] answer, I have not seen it but I thought at the time Diogo got the ball and kicked it out. I did not think for one second it was a bad challenge. I got told later it was a lack of force [that meant he was not shown red].”
