With hindsight, the difference between automatic qualification and the play-off route was their opening game in the Netherlands.
The visitors took an unlikely two-goal lead through Robbie Keane and Jason McAteer, before two goals in the final 20 minutes meant the game ended in a draw.
Their next game was no less difficult - a trip to eventual group winners Portugal.
But a worthy draw kept their hopes alive and the Irish managed to comfortably win the supposedly easy games against Cyprus, Andorra and Estonia.
During the matches, McCarthy found out that captain Roy Keane was as valuable as ever, while discovering a new rising star in Matt Holland of Ipswich.
Without doubt, the most memorable win came at home to the Netherlands.
Down to 10 men, the Irish saw Jason McAteer appear from nowhere to slot home a half-volley and enable them to gain revenge for their 1994 exit by the Dutch.