In 1970, Marichal experienced a severe reaction to penicillin which led to back pain and chronic arthritis. Marichal's career stumbled in , when he only posted 12 wins and his ERA shot up to 4.12, before straightening itself out with a stellar 1971 season in which he won 18 games and his ERA dropped below 3.00. It was the only season in which Marichal earned any consideration for the Cy Young Award, finishing in 8th place. The Giants returned to the playoffs for the first time since 1962, winning the NL West division and facing the Pittsburgh Pirates in the NL Championship Series. Marichal started the third game of it and pitched well, limiting Pittsburgh's offense to solo home runs by Bob Robertson and Richie Hebner. However, the Giants managed only one run, losing the ballgame 2–1 before losing the series three games to one. 1971 was Marichal's final great season (and his final of 10 All-Star appearances), however. In 1972, he got off to a 1–6 start, finishing the season with a 6–16 record. After posting an 11–15 record in 1973, he had his contract sold to the Boston Red Sox on December 8.