Briles spent most of his first season in Pittsburgh in the bullpen, however, was added to the starting rotation in September. Though he pitched very well, (3-1 with two shutouts, a complete game and a 1.74 ERA) he did not make an appearance in the 1971 National League Championship Series against the San Francisco Giants. He did, however, earn a game five start in the 1971 World Series against the Baltimore Orioles. With the series tied at two games apiece, Briles pitched a brilliant two-hitter to carry the eventual World Champions to a 3-2 series lead. He also drove in a run with a second inning single. He pitched three seasons for the Pirates, going 36-28 with a 2.98 ERA.