After Sisler graduated, "magna cum laude", he was signed by the Boston Red Sox of the American League (AL), and began his professional baseball career at the age of 21 in 1953 for the Albany Senators in the class-A Eastern League. He pitched in 21 games that season, 20 as their starting pitcher; he had a 12–7 win–loss record and an ERA of 2.60 in 135 innings pitched. He was the last pitcher from Princeton to start a major league game until Chris Young in 2004.