With several new players joining City, it is only a normal resulys, that City still need a process to win games and made more solid team. this defeat will give guardiola a very good thing to fix the squad and formation in order to achieve the best results. It's still one game, not reflecting failure to the end. After a few games, i believe guardiola will find his best formation, and from there City will start to rise.
I read posts, and it seems that people have already buried Manchester City, and no one believes in them... The season has just begun, the first game. Maybe it didn't work out so well, but at the helm of Pep and, as you said, he will find the right scheme, replace players, etc. He has always solved problems, even worse than these. So believe me, the City will fight for the rest of the season.