After his military commitment, he re-joined the organization, and began the season with the Red Sox. He made his major league debut on April 26, 1956, a one-inning relief appearance against the New York Yankees. His first MLB victory came seven days later, a three-inning relief appearance against the Yankees in Boston. On August 5, in his sixth start, he pitched a seven-inning complete game 2-1 victory over the Cleveland Indians and their pitching star, future Hall of Famer Bob Lemon. In total, he appeared in 39 games his first season, 14 as their starting pitcher, had a 9–8 win–loss record with three saves, 98 strikeouts, and a 4.66 ERA in 142⅓ inning pitched. He tied for the AL league with a 1.000 fielding percentage by not committing a single error, although he had the sixth highest total of hit batsmen with seven. Following the season, Sisler was praised for his performance; he was selected by Boston area sportswriters as the "Harry Agganis Award" winner, given annually to whom they voted as the top Boston Red Sox rookie, and was named to the 1956 "Rookie All-Star Team".