The forward caught the entire visiting defence off guard with a back heeled finish to double our advantage half an hour into proceedings, having already found the breakthrough himself inside 5 minutes.
After ending a 12-year wait to win the FA Youth Cup in November’s 3-2 final victory over Chelsea, City wasted no time in getting on the front foot in their first match of this season's competition.
Our Young Blues dominated possession from the off, and were rewarded inside five minutes when Delap was sent clean through on goal after smart link-up play with Robertson.
In what is becoming a familiar sight, the forward shifted the ball onto his right and calmly slotted home under the despairing dive of Aaron Clayton to hand Carlos Vicens’ side the advantage.
And we never looked back from that point, confidently zipping the ball around with a typical flair and intensity on the pristine Academy Stadium turf.
McAtee was next to threaten, shrugging off the challenge of Kade Craig before eventually winning a corner on the right after ten minutes.
Finley Burns rose highest from that subsequent set-piece, forcing a smart save from Clayton low to the ‘keeper’s left.
After coming away relatively unscathed from that initial onslaught, Birmingham tentatively grew into the game, looking to frustrate City in three solid defensive banks and show why they sit top of the Professional Development League North.
But Carlos Vicens’ side continued to peg the visitors back inside their own half, with Samuel Edozie flashing a near-post effort over the bar after being fed by Bobb.
And the winger went close again just before the 25-minute mark, latching on to Juan Larios’ incisive through ball down the left, but he was smothered by a combination of Clayton and Callum Sullivan before he could pull the trigger.
Against the run of play, Birmingham’s first real chance of the half fell to Amari Miller just after the half hour.
The winger was forced to the byline by Burns, but opted to try and catch out Mikki Van Sas with a cheeky low finish at his near post rather than squaring the ball.
However, our stopper was up to the task and saved well with his feet to prevent an unlikely equaliser.
City soon had some breathing space as the end of the first half approached, with a moment of brilliance from Delap lighting the blue touch paper in the 36th minute.
Bobb caused havoc down the Birmingham left, creating some penalty box pinball which eventually saw McAtee square it to our centre-forward.
Delap, facing away from goal and being marked tightly, caught everyone unawares by nonchalantly back heeling the ball into the bottom corner of the net.
And before the visitors could compose themselves it was three, Bobb finding a pocket of space on the right before firing in at the near post just two minutes later for his third goal in as many days.
The rain began teeming down at the Academy Stadium as the second 45 got underway, and City had their sights set on opening the floodgates.
With the half less than two minutes old Robertson added a fourth, racing onto McAtee’s impressive lob over the top to poke home under pressure from Marcel Oakley.
And the midfielder returned the favour on the hour, winning the ball back on the high press and squaring for McAtee, who confidently found the top corner from around the penalty spot.
With the game reaching the final stages, Egan-Riley added number six, latching on to substitute Kwaku Oduroh’s searching cross and coolly side-footing home with ten minutes to play.
Despite our dominance, a late chance fell to the visitors when Joshua Williams was sent through with just Romeo Lavia to beat, but our anchorman expertly cut out the danger, blocking a rasping drive to preserve the clean sheet.
However, the winger was not to be denied a second time, smashing home a late consolation through a crowd of bodies.
Despite that late setback, it was a five star performance from our Young Blues, who will rightfully be delighted with how their FA Youth Cup campaign has got underway.
How we lined up
Lavia sat in front, with Robertson and McAtee completing the midfield three.
At the sharp end, Bobb and Edozie provided width for Delap.
City XI: Van Sas, Egan-Riley (c), Doyle (Oduroh), Larios, Burns, Lavia, Robertson, McAtee (Borges), Bobb, Edozie, Delap (Sodje)
Subs: McNamara, Adam, Griffiths, Hamilton
Birmingham XI: Clayton, Dugmore, Oakley, Craig, Sullivan (Noakes), Chang (c), Hall, James, Williams, Miller, Wakefield (Walker)
Subs: Brooks, Manton, Fogarty, Barratt, Nguepissi
Carlos Vicens’ Young Blues will host either Everton or Wigan Athletic in the fourth round of the FA Youth Cup, with the ties scheduled for Saturday 3 April.
It’s a quick turnaround in the Under-18s Premier League, however, with a trip to Derby County next on the cards in midweek.
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