After just one season in the minor leagues, Cochrane was promoted to the major leagues, making his debut with the Philadelphia Athletics on April 14, 1925 at the age of 22. He made an immediate impact by becoming Connie Mack's starting catcher in place of Cy Perkins, who was considered one of the best catchers in the major leagues at the time. A left-handed batter, he ran well enough that Mack would occasionally have him bat leadoff. He hit third more often, but whatever his place in the order his primary role was to get on base so that hard-hitting Al Simmons and Jimmie Foxx could drive him in. In May, he tied a twentieth-century major league record by hitting three home runs in a game. He ended his rookie season with a .331 batting average and a .397 on-base percentage, helping the Athletics to a second-place finish.