And the Under-23s prevailed in the shoot-out, with Jake Weaver saving one spot-kick, to squeeze through to the Third Round.
It was tough on Midland Football League Premier Division side Highgate, who more than gave as good as they got.
But on the other hand it was a real show of character by Richard Beale's young side, who included 16-year-old Academy scholar Tom Anderson making his debut and two trialists.
Wes McDonald calmly slotted the final equaliser of the night with six minutes remaining, after the ball ran through to him from Jack Storer to the left of the area.
And the same player could have won in at the death, instead skewering wide from close range after a brilliant surge down the right and precise cut back by the dynamic Corey O'Keeffe.
But the tie was decided on penalties and Storer's successful opening kick was cancelled out by Isaac Jagroop's effort.
Olly Mulders was next up but his firmly struck attempt, high to the left, went over off the crossbar so when Josh Hawker despatched Highgate's next penalty, Blues were 2-1 adrift.
Beryly Lubala found the bottom corner to make it 2-2 before Weaver pulled off a fine save, a firm hand going quickly skywards to deflect away a driven penalty by Lei Brown.
Anderson showed his coolness to make it 3-2 to Blues by putting his penalty low past the 'keeper.
The eighth kick of the shoot-out proved critical as Aaron Brown walloped his high into the night sky over the crossbar.
That meant McDonald could clinch it for Blues and he duly did, another well placed shot into the corner.
Blues celebrated in joy, relief and in the knowledge that they had come through a very testing encounter.
Ironically, they could easily have been a goal up inside the opening few seconds when trialist Ollie McCoy burst in and dragged a shot wide from the right of the area. Then David Popa stabbed past the post before Storer took a shot early on the move and whacked it just over the crossbar.
But Blues whirlwind start was dampened by Highate after they settled and imposed themselves on a contest that was not for shrinking violets.
McCauley Manning served notice of the hosts intent and by cracking a fine curving shot off the crossbar in the 13th minute.
Blues might have scored through Popa after a fine counter-attack, but he was forced a little wide by a strong tackle and couldn't get the required power or direction needed.
Highgate took the lead from a Hawker free-kick met by decisively by a Scott Turner header that looped beyond Weaver (37 minutes).
However, just 40 seconds later Blues were level when Storer cut back onto his left foot and let rip with a shot that went in via a deflection.
It remained level at the break but with the promise of more twists to come as fog began to settle over Highgate's Coppice ground in Shirley.
And sure enough Highgate, who subjected Blues to trial by set-piece after the break, took the lead once more, in the 52nd minute, when Manning's low shot from the edge of the area bobbled back off the post, was retrieved at the byline by Marco Adaggio and turned into his own net by the unfortunate trialist Elliot Kebbie.
Blues responded by forcing a save, with his feet, from Brendon Bunn, after substitute Lubala cut inside from the left following spadework by Storer.
A second equaliser came in the 62nd minute after McDonald attracted the attention of three defenders on the left of the area, set Mulders up for a cross-shot that was parried out by the 'keeper, leaving McCoy to dart in and stick away the loose ball from close range.
Highgate threatened next through a powerful Dale Edwards shot that was repelled before an exquisite pass by Anderson sent Lubala away, but he was unable to round Bunn, who snared the ball at his feet at the second attempt.
That let off for Highgate looked to have been costly as, in the 75th minute, Turner headed a back post free-kick goalbound and although Weaver got a hand out to parry the attempt up, James Loney came flying in with a diving header to force the ball over the line.
Blues were down, but not out. McDonald restored parity during a very strong finish to the match by a Blues side encouraged from the sidelines by the rest of the Under-23s, the Club's Under-18s as well as Academy coaches and staff.
As added-time loomed, McDonald missed a golden chance and also hoisted another shot beyond the crossbar following an Anderson run as Highgate tottered.
But as it turned out, Blues saw it through in the penalty shoot-out, a dramatic way to decide a hard-fought and absorbing match.
Blues: Weaver, Kebbie, Mulders, Maxwell, Martin, Anderson, O'Keeffe, McCoy, McDonald, Storer, Popa (Lubala 56). Not used: Trueman, Ebbutt, Stirk, Kwiecien.