 O'Flaherty made his debut in the major leagues on August 16, 2006, against the Oakland Athletics.He pitched 2/3 of an inning, faced 4 batters, allowed one hit, one walk, and got his first strikeout in the major leagues.On the same day of O'Flaherty's debut, the Seattle Times reported that his "big-league visit was too short to qualify as a cup of coffee".