The Blues dominated the first half with an impressive attacking display and battled hard in the second to hang on for a 2-1 victory, thanks to goals from Kevin De Bruyne and Kelechi Iheanacho.
The manager, celebrating the continuation of his 100% record, told press his side deserved the win and expressed his pride for their individual and collective performances.
“The first half was really good,” he stated. “The last minute was a fantastic goal from Zlatan Ibrahimovic.
“In the second half, we knew they would change the system – they put Paul Pogba and Marouane Fellaini more in front and they were much stronger.
“The second half was an open game. We had many counter-attacks. When you have three on three, four on four, five on five, you have to take advantage because in the last minutes, anything can happen.
“We played good. We had the ball and when we lost it, we won it back quickly. We created enough chances.
“You cannot come to Old Trafford and dominate. It’s impossible.”
Guardiola also reserved praise for defensive duo Aleks Kolarov, Nicolas Otamendi and debutant goalkeeper Claudio Bravo.
He added: “The central defenders – Aleks and Nico - were outstanding.
“What Claudio did was one of the best performances I’ve ever seen. I like goalkeepers to play in front and after that [United] goal, he continued playing in our build-up, playing long balls and coming out to pick it up.
“In football, it’s about how you react to mistakes – it shows character. He continued playing. It means a lot.
“The way we train and the way we play has given me a lot of confidence.
“We played good in the first half because of Claudio. I like the keepers to attack the ball and after what happened, in the second half he continued to play and that’s a good thing about his personality. He was one of the reasons we played well in the first half.
“Yeah [if you pass the ball from the back] it can be too risky; if you lose the ball they will score but you can control the game.
“Until my last day in England I will try to play with the ball as much as possible. I know it’s impossible for 90 minutes but I’m sorry, I will not negotiate that.
“Today we made a lesson with the ball.”