In 1990 McCarthy returned to the Cork senior hurling team as assistant coach and trainer with Fr. Michael O'Brien. The Rebels faced reigning All-Ireland champions Tipperary in the provincial decider that year, however, Cork's chances were dismissed by Tipp manager Babs Keating. His statement that "donkeys don't win derbies" severely riled the Cork team, so much so that they won the Munster final convincingly by 4–16 to 2–14. The subsequent All-Ireland final saw Cork installed as underdogs against Galway. In one of the most open and exciting finals of the decade Cork steamrolled back from a seven-point deficit at half-time to win by 5–15 to 2–21.