In 1972, O'Leary had his first senior success when he won a National League medal following a 3–14 to 2–14 defeat of Limerick. He later added a Munster medal to his collection following a 6–18 to 2–8 thrashing of Clare. Old rivals Kilkenny provided the opposition in the subsequent All-Ireland final on 3 September 1972. Halfway through the second-half Cork stretched their lead to eight points. Kilkenny's great scoring threat Eddie Keher was deployed closer to goal and finished the game with 2–9. A fifteen-point swing resulted in Kilkenny winning the game by 3–24 to 5–11.
