1- Kevin De Bruyne and Fernandinho dominant
De Bruyne and Fernandinho were both rampant against a fairly open Manchester United midfield popping up in different places on the pitch and making dangerous runs in the first half. Fernandinho turned into last ditch defender late on and as usual carried out his task with minimal fuss and maximum effectiveness. De Bruyne was sublime and very easily could have had a hat trick. For Manchester United., Paul Pogba's poor sense of positioning opened the game up for KDB.
2- United's pace became a problem in the second half
The Blues had trouble coping with Manchester United's pace after Marcus Rashford came on at halftime. When Anthony Martial came on late desperate defending became the norm. City's wide players were pinned back and were unable to maintain possession in healthy doses very often in the second half. In retrospect, Pep Guardiola's quick decision to insert Fernando probably saved the victory for the Blues as he was able to provide adequate cover for the back four which was becoming increasingly stretched.
3- Claudio Bravo
A rocky debut for the world-class keeper but given his pedigree we can only assume things will get better. This was a difficult spot to start his City career and in retrospect perhaps he was thrown into the deep end too quickly.