While Guardiola would have been happy with their build-up play, the quality finishing was surprisingly poor and only Raheem Sterling had found the target with a powerful effort, as Riyad Mahrez twice went close.
Having spent so long defending for their lives, Newcastle’s hard work was undone by a moment of madness after 37 minutes.
De Bruyne’s cross-searched for Gabriel Jesus but the Brazilian found himself on the deck after a shove from Javi Manquillo
Referee Lee Mason hadn’t spotted the incident, but a word from VAR official Andre Marriner helped him make the decision.
De Bruyne took responsibility for the spot-kick and made no mistake, slotting into the corner and sending Karl Darlow the wrong way.
As 1-0 leads went, City could not have done more to deserve theirs at the break and Newcastle knew had to change their shape or face another onslaught in the second half.
Steve Bruce’s side did push up the pitch and began to cause City some problems, although the visitors missed golden opportunities through Mahrez and Gabriel Jesus to make their lives more comfortable.
Then came the game-changing moment. Allan Saint-Maximin, Newcastle’s brightest player, ran down the right and delivered a pinpoint cross for substitute Dwight Gayle.
With the goal at his mercy and only six yards out, the striker somehow lifted over from six yards out and with it, Newcastle’s chance had gone.
Within 90 seconds of that chance, City punished Newcastle by doubling their lead. Aymeric Laporte fired into Phil Foden and he found Sterling, who cut inside and bent his effort into the far corner from 20 yards.