A Riyad Mahrez double after the break ended Fulham's hopes of an upset in what was an open, entertaining encounter played in front of a full-house at the Etihad.
It was a breathless start.
Arguably two of the most attack-minded teams in the country, both topping their respective divisions, it seemed goals were guaranteed.
What wasn’t expected that there would be three goals inside the first 13 minutes – and there could have been two or three more in that frantic opening.
Jack Grealish could have scored inside the opening minute, but it was Fulham who scored with their first attack as a clever pass out to Harry Wilson saw his low cross from the right turned in by Fabio Carvalho from close range.
Fulham continued to attack with purpose, but the Blues struck again seven minutes later with a rare goal from a corner.
The game settled down thereafter, with fewer openings in a fairly even contest that saw the Blues go in at the break with a 2-1 lead.
Whatever tactical tweaks Pep Guardiola made at the break, the game was as good as over within 12 minutes of the re-start.
City's third came when Grealish's mazy run into the box was ended by a crude Joe Bryan challenge and Mahrez tucked home the resulting penalty.
Then, four minutes later, the Algerian winger was played in by De Bruyne and his shot struck Harrison Reed on its way into the bottom left corner.
We may have to wait for the dubious goals panel to decide who is credited with that one.
With less than an hour played and a 4-1 lead, Guardiola was then able to bring on fresh legs with Wednesday's game against Brentford in mind.
There were several half-chances in the final half-hour and Liam Delap, back after several months out, was denied a fine headed goal by the assistant referee.
But ultimately, it was a comfortable victory for City who edge ever closer to another Wembley date.
Two goals and an assist win Riyad Mahrez the man-of-the-match award.
Fulham: Gazzaniga, Williams, Tosin, Reed (Seri 67), Bryan, Chalobah, Reem, Wilson (Cairney 75), Carvalho (Cavaleiro 88), Kebano (Knockaert 67), Mitrovic (Muniz Carvalho 75)
Substitutes: Rodák, Hector, Onomah, Mawson
What it means…
City are into the FA Cup fifth round which will be played the week commencing 28 February.
The draw will take place live on ITV on Sunday afternoon prior to Liverpool's game against Cardiff City.
City return to Premier League action against Brentford next Wednesday, February 9 with a 19:45 (GMT) kick-off at the Etihad.
"I am going to tell you something, I know exactly which team we faced today and which team we beat.
"When a team is top of the Championship, it is because they are good. Top side, Marco has created an incredible team.
"We spoke a lot with the players about how difficult it would be and we should fight and run and defend well.
"They are a team who monopolise the ball. The first half the pressing was not good, that was my fault because we expected one movement that didn’t work well.
"The second half was much better and of course the quality of our players made the difference.
"We are very pleased to be in the next round. This round showed us there can be many surprises and we won against a very top team."
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