In the 1929 season, Pennock saw his pitching time and pitching quality diminish. Over the rest of his career, he never posted more than 189 innings pitched in a season and his ERA rose to over 4.00. He suffered from bouts of neuritis in 1929 and 1930. Pennock won his 200th career game during the 1929 season, becoming the third left-handed pitcher to reach that mark. He led the AL in walks per nine innings pitched in 1930 (1.151) and 1931 (1.426). Pennock pitched four innings of relief against the Chicago Cubs in the 1932 World Series, recording two saves. The New York chapter of the Baseball Writers' Association of America named him their player of the year.