McCarthy's first appearance, as a 17-year-old to whom the gathering of 1,002 seemed "a big crowd", was nearly his last. He was allowed to drift off to college in Nottingham, where he subsidised his rent by earning pounds 25 a game from Shepshed Charterhouse while consoling himself that he at least had played League football.
And that might have been that had the management duo who gave him his debut, John Bird and Alan Little, not resurfaced at York two and a half years later. When their small squad was depleted by injuries, they remembered McCarthy. The student winger seized his second chance.
As befits a late starter, he has crammed more into the ensuing years than most players do into two decades. A bronze medal from the World Student Games was followed by promotion with York. Then came a pounds 450,000 transfer to Port Vale and World Cup combat with Northern Ireland.
Last September brought a pounds 1.5m switch to Birmingham, equalling their highest outlay, and with it the possibility of Premiership football. On Saturday the First Division play-off contenders will be striving to reach the FA Cup quarter-finals at the expense of Leeds, a contest which the 27-year-old Teessider awaits with even greater anticipation than usual.
One reason is the prospect of matching his progress against that of David Wetherall, a team-mate and friend from the British student side who is now vice-captain and defensive mainstay for the Yorkshire club. He is also determined to make more of his second experience of the fifth round than he did of the first, which by coincidence was also against Leeds.
"David was the one who stood out in the 1991 Games in Sheffield," McCarthy recalled. "He'd just been transferred from Wednesday to Leeds and you could already see he had that something extra.
"He had to speak at the opening ceremony because he was the local boy. I remember it well because Helen Sharman, the British astronaut, dropped the torch and the flame went out!''
Britain reached the semi-finals before losing to the Dutch. They beat Uruguay to take third place, after which McCarthy, by now a BSc in Sports Science, graduated to the full-time ranks at York.
John Rudge made him Vale's record buy in 1995. It was hardly the most glamorous of moves - "no one else wanted me," McCarthy said with disarming candour - but within six months circumstances conspired to bring his blend of touchline trickery and hard graft to a wider audience.
The Potteries club forced a deserved draw at Everton, then the FA Cup holders. "Only a handful of ties were played because of the weather. Goodison Park has undersoil heating, so ours was one of them.
"All the postponements meant it also became Match of the Day. I had one of my best games and Trevor Brooking highlighted some of the things I did that night. What a difference one programme can make.''
McCarthy's reputation was further enhanced when he scored the winner in the replay from a cross by fellow winger Steve Guppy - now of Leicester and England B - to earn a reunion with Wetherall at Elland Road.
"We were the better team in a 0-0 draw and I went from hero to villain by missing a good chance. We went a goal up at Vale Park, but once Gary McAllister equalised Leeds just kept getting stronger and won 2-1.''
It was then that he was claimed by Northern Ireland, his grandmother's birthplace. Although Keith Gillespie remains first choice in his position, McCarthy's cap collection includes one gained against Italy - Maldini, Zola, Casiraghi, Del Piero et al - amid the firecrackers of a Sicilian friendly last winter.
Even then, Trevor Francis' interest was an open secret. Once, McCarthy was walking near his home in Cheshire when a Birmingham exile on a bike pulled up and demanded to know when he would be signing. Within months the deal had gone through, one of Francis' 40 in 20 months, but there was to be no overnight success.
"When I first joined Vale they failed to win any of the opening 10 home games. It was a club record. I made my Birmingham debut at home to Sunderland when a win would have put us top. We lost, and won one of the next 15 to end up in mid-table.''
Dubbed "The Jinx" by one fog-horn fan, McCarthy gradually won over the St Andrew's crowd. Last month's stunning 7-0 win at Stoke underlined his growing influence on a fast improving side, though the sight of an ex-Vale man crashing in No 5 did not go down well with the locals.
"I'd turned away to celebrate with Paul Furlong when, apparently, this fan charged on to the pitch to have a go at me. Chris Marsden pushed Larus Sigurdsson [Stoke captain] towards him and he stopped him. One report said it was the most effective marking he did all afternoon.''
Last weekend's draw with Middlesbrough, in which McCarthy scored against the club he idolised as a boy, found Francis' team in the kind of form that could trouble Leeds. The Premiership outfit struggle to break opponents down at home, whereas Birmingham have tended to travel well.
For the level-headed McCarthy, whose own odyssey began so inauspiciously at Hartlepool, the tie is a reminder of how far he has come as well as how close the winners will be to Wembley.Reuse content