Here are four things we learned from the game at Old Trafford...
1 Maffeo can challenge senior stars
Pablo Maffeo was one of the stars of the show against United, delivering a solid performance at right-back and keeping the in-form Marcus Rashford quiet for much of the game.
It was a timely reminder of his capabilities. Bacary Sagna is currently out having suffered a hamstring tear playing for France earlier this month and Pablo Zabaleta is still recovering from a foot injury sustained against Barcelona.
Maffeo, 19, gave a display that suggests he is ready to step in on a more regular basis.
2 Garcia possesses real quality
Another 19-year-old also impressed.
Aleix Garcia was the star of round three as City beat Swansea – and he repeated the trick in round four against United by delivering another assured, accomplished display.
The Spanish youngster sat deep and sprayed the ball around, demonstrating his ability to pick passes, both long and short, and keep City in possession.
Guardiola, a man obsessed with build-up play, will no doubt have been hugely impressed.
3 Rotation should leave Blues squad fresh
With City facing a packed fixture schedule in the coming weeks, it made sense for Guardiola to freshen things up for this game.
Nine changes were made from the side that drew 1-1 with Southampton at the weekend.
That should benefit the squad with games coming thick and fast.
4 City need a result
It’s now six matches without a win for City – the first time since 2008 they have endured a winless streak that long.
The good news for Guardiola is the quality of City’s football during that period has largely been impressive.
A win is needed, though. Next up: West Brom on Saturday.
