Pennock received only one start apiece in the months of April and May, as the 1919 Red Sox relied on George Dumont, Bill James, and Bullet Joe Bush, leading Pennock to threaten to quit in late-May unless Barrow fulfilled his earlier promise to Pennock. Barrow continued to use Pennock regularly after Memorial Day, and Pennock finished the season with a 16–8 win–loss record and a 2.71 ERA in 219 innings pitched. He served as the team's ace pitcher in the 1920 season, but subsequently settled in as the Red Sox' third starter. After the 1922 Red Sox campaign, in which he went 10–17, and had seven wild pitches, leading the AL, the New York Yankees began to negotiate with the Red Sox to acquire Pennock. The Yankees traded Norm McMillan, George Murray, and Camp Skinner to the Red Sox for Pennock that offseason.