In all, the home side fielded nine reserves - 10 if you include David Platt - who could not have provided a better demonstration that enthusiasm is no substitute for experience.
After 120 minutes, the junior Gunners made it into the fourth round but not nearly as cosily as the scoreline might suggest. Certainly, it was a rough introduction, too, for Alex Manninger, replacing David Seaman in goal. His first attempt to claim a cross missed by several feet, and his second touch of the ball was to remove it from the net after 20 minutes.
Rare indeed is the Arsenal defence that struggles to clear crosses, but when Martin Grainger's free-kick from the right was headed down to a red and white shirt on the six-yard line, it was casually trundled out to Tony Hey, who thumped it back past Manninger.
Most surprising of all, it was Lee Dixon who fluffed the clearance, and with their most senior colleague showing such uncertainty, his younger companions could hardly be blamed for following suit.
Luis Boa Morte's aggression down the left often threatened, but Steve Bruce and Gary Ablett smothered most openings, while behind them Ian Bennett was equal to those they did not.
That the home side were still in the match with half an hour left to play was due only to a mixture of bad fortune and worse finishing on Birmingham's behalf. First, Grainger shaved the bar with a free-kick from 25 yards which deserved much better, before Paul Devlin somehow managed to miss the target when the ball had feet rather than yards to travel.
Punishment was just minutes in coming, as Bruce returned Dixon's earlier generosity with a weak headed clearance, which sat up for Boa Morte to score from 18 yards. Now Arsenal attacked with belief and only a superb sliding tackle by Bruce stopped Boa Morte's run on goal a few minutes later.
An even better chance went begging at the other end, however, as another dreadful pass by Dixon sent Devlin clean through, but his shot was a couple of yards wide.
Wreh could have spared Arsenal extra time when his shot from the edge of the area after 80 minutes brushed the bar, and it seemed Arsenal would to enjoy their proverbial good fortune when Darren Wassall was sent off for a professional foul on Boa Morte five minutes later.
Extra time brought the Arsenal debut of 19-year-old Jason Crowe. He got his first kick at senior level after ust 90 seciodns, but sadly it connected with Birmingam's Martin O'Connor, on the edge of the area, and Crowe was straight back off again.
Three goals in 10 minutes then secured Arsenal's progress. Platt scored from the spot after a trip on Boa Morte, and it was the impressive Boa Morte himself who added the third before Alberto Mendez completing the scoring.
Arsenal (3-5-1-1): Manninger; Grimandi, Upson, Marshall; Dixon (Crowe, 91), Platt, Hughes, Vernazza, Boa Morte (Muntasser, 119); Mendez; Wreh. Substitute not used: Bartram (gk).
Birmingham City (3-5-2): Bennett; Wassall, Bruce (JOhnson, 101), Ablett; Grainger, O'Connor, Hey, Holland (Francis, 106) Robinson; Ndlovu, Devlin (Bass, 85).
Referee: U Rennie (Sheffield).