A quick first half was enough for Manchester City to book their place in the fourth round of the FA Cup.
Two early goals from Bernardo Silva put the hosts in firm control of the contest, before Phil Foden made it three just past the half hour mark.
Both sides rung the changes in the second half, as the Citizens kept their fine run of form going ahead of a crucial run of Premier League fixtures.
Story of the Match
Pep Guardiola has made no secret of his love for the oldest competition in club football, and neither has Manchester City owner Sheikh Mansour, who earlier this week purchased the oldest remaining FA Cup trophy.
And that love for the competition was evident when the team sheets came out, with Manchester City fielding a starting XI to rival any, with Kyle Walker and Gabriel Jesus returning to the side after missing the last fortnight due to COVID-19 protocols.
It took no time for the competition favourites to get going either, as Bernardo Silva opened the scoring after just seven minutes, in quite spectacular fashion.
George Friend's headed clearance fell to the Portuguese international on the edge of the box, and, despite the ball sitting at an uncomfortable height for a first time effort, Bernardo fired a half volley into the top corner to grab his first Manchester City goal of the season.
And one soon became two, this time in trademark Guardiola fashion.
The move started with a fantastic outside of the foot pass from Riyad Mahrez, who found Kevin De Bruyne's run towards the baseline. The Belgian then cutting the ball back into the box towards the onrushing Bernardo, with the Portuguese given the simple task of turning the ball into the back of an unguarded net.
It was almost training ground stuff as the half wore on, with Manchester City adopting a three at the back formation in possession, as Joao Cancelo was given somewhat free reign to roam the midfield to offer an extra outlet in attack.
The hosts made it three just after the half hour mark, with the inform Phil Foden getting himself on the scoresheet with a low drive from the edge of the box that left Andres Prieto with no chance.
There was little in the way of Birmingham City chances in the first 45, as the goal shy Championship club found themselves three goals adrift at the break.
Both sides rung the changes at half time, with the hosts brining on John Stones, Taylor Harwood-Bellis and Felix Nmecha in place of Ruben Dias, Joao Cancelo and Kevin De Bruyne. Whilst Birmingham brought on former Manchester City youngster Adam Clayton and Marc Roberts in place of Scott Hogan and Jon Toral.
The second half began as the first had finished, with the hosts dominating the possession of the ball as Birmingham sat deep in order to avoid any further damage to the scoreline.
It looked as though Manchester City had furthered their lead on the hour mark, as Mahrez got on the end of Rodri's clipped ball over the top, however the assistant's flag was raised, with replays showing the Algerian was fractionally offside.
Both sides made changes as the half wore on, Fernandinho and Liam Delap replacing Rodri and Gabriel Jesus for the hosts, with Johnathan Leko and Ivan Suvic making way for Lukas Jutkiewicz and Jeremie Bela for the visitors.
There was little more to report in terms of chances in the second half, with the pace of the game slowed drastically as Manchester City cruised their way into the hat for the fourth round of the FA Cup.
Bernardo is back
It's been a tricky twelve months for Bernardo following an outstanding 2018/19 campaign, with the Portuguese international struggling for form following a suspension over a tweet directed at his teammate Benjamin Mendy.
And after struggling for minutes through the early stages of the campaign, Bernardo has soon found his feet again and highlighted his return to form with two outstanding goals on a routine afternoon for the hosts.
Cancelo's the man
Another player who has returned to form is Bernardo's international team mate, Joao Cancelo.
The fullback struggled for minutes in the 2019/20 campaign, but after impressing at left back in the latter stages of last season, he has grown to be one of the first names on Pep's team sheet this term.
His versatility and impressive work rate has been a key to City's turnaround in form, and he's sure to be a big player in the second half of the season.
Birmingham's goal struggles continue
Let's face it, few fancied Birmingham to come to the Etihad and get a result today.
But another blank next tot eerie name on today's team sheet means that Aitor Karanka's men have now gone four games without scoring as they sit a lowly 18th in the Championship.
They'll be hoping to turn that around, and fast, as they visit Middlesborough in the Championship this Saturday.