By 1978 O'Hara was a member of the Kilkenny senior team. He lined out in his first Leinster final that year with Wexford providing the opposition. The game developed into a close affair; however, victory went to ‘the Cats’ by 2-16 to 1-16. It was O'Hara's first Leinster title. Following a subsequent victory over Galway in the All-Ireland semi-final Kilkenny faced arch-rivals Cork in the All-Ireland championship decider. Much was at stake as Cork were aiming to capture a third All-Ireland victory in-a-row and nothing would give Kilkenny greater pleasure than stopping them. Both sides remained neck and neck for much of the game, however, Cork gradually grinded down the opposition. Cork’s Jimmy Barry-Murphy scored the winning goal for Cork with thirteen minutes left in the game.