Foster was immediately inserted into the starting line-up in center field, as starting center fielder Bobby Tolan was lost for the season with a torn Achilles tendon. He returned to a back-up role in , platooning in right field with César Gerónimo, and managed just a .200 batting average, two home runs and twelve RBIs. The nucleus of the "Big Red Machine" began coming together that season, however, and the Reds returned to the post-season playoffs after a disappointing fourth-place finish in 1971. Foster played in the 1972 National League Championship Series against the Pittsburgh Pirates only as a pinch runner for Tony Pérez in game five of the series; he scored the series-winning run on a wild pitch from Bob Moose. Foster appeared in games one and five of the World Series against the Oakland Athletics, but did not log an at-bat.