Man City could have added more to their tally but goal-line technology was called into action to deny them.
Four minutes later, the in-form Kevin De Bruyne created the second, powering down the right flank and delivering a pinpoint low cross to Gabriel Jesus, who made no mistake. If we don't play good we can not beat that team, it's impossible. De Bruyne hammered a volley onto the underside of the crossbar in the 26th minute - seeing it land on the wrong side of the goal line - before Jesus' effort on the turn was blocked on the line by Koulibaly and cleared, with replays showing the ball did not go all the way over.
Despite losing two of their three games in the Champions League, Napoli have made a flawless start to Serie A with eight wins out of eight. "It's one of the wins I'm most proud of in my whole career". They can break with a lot of speed, as they showed in this game. "Napoli, for the way they play, of course they can win the league".
Guardiola has good reason for optimism, given the form of his attacking players, not least De Bruyne, for whom two moments stood out in a brilliant individual performance.
Midfielder of Turkish origin Ilkay Gundogan will have to continue waiting for his first Champions League start of the season as he also starts on the bench.
"I think it was an extraordinary game from both sides".
He said: "In the coming months I'll meet with City to figure out how to improve and extend his contract".
"We are scoring goals, making assists and winning games and that is the main thing".