He was 2-0 with a 3.18 ERA for the Cards when they dealt him mid-season to the San Francisco Giants for Frank Linzy. With the Giants, Johnson emerged as one of the top relievers in the National League, finishing sixth in Cy Young Award balloting during an era when such an honor was rare for relief pitchers. In , Johnson went 12-9 with a 2.97 ERA and eighteen saves for the division winning Giants. In his only post-season, he pitched 1.1 innings and gave up two runs to the Pittsburgh Pirates in game four of the 1971 National League Championship Series.