Koosman also made the first of two All-Star teams in his career. The National League won the game 1–0 (to date, the only All-Star Game to end in a 1–0 score) in the "Year of the Pitcher." Koosman pitched a scoreless ninth for the save, striking out Carl Yastrzemski for the final out. Koosman was named to the 1968 Topps All-Star Rookie Roster and finished runner-up to Johnny Bench for the National League Rookie of the Year honors. The Miracle Mets  In  Koosman posted a 17–9 record with a 2.28 ERA and 180 strikeouts in another All-Star season. That year, he was a member of the Mets team that unexpectedly won the National League East title (both leagues had split into two divisions after expanding from ten teams to 12) after not only finishing dead last in five of their first seven seasons, but also trailing the Chicago Cubs for much of that season by as many as 9 games. After Koosman lost to the Houston Astros to fall to 9–8, he won eight of his final nine decisions. In Game Two of the NLCS against the Atlanta Braves, Koosman was shelled for six runs in 4 innings (including a Hank Aaron three-run homer). The Mets won 11–6, however, then won the next game to complete the series sweep. Koosman was the pitching star of the 1969 World Series against the Baltimore Orioles.
Koosman also made the first of two All-Star teams in his career. The National League won the game 1–0 (to date, the only All-Star Game to end in a 1–0 score) in the "Year of the Pitcher." Koosman pitched a scoreless ninth for the save, striking out Carl Yastrzemski for the final out. Koosman was named to the 1968 Topps All-Star Rookie Roster and finished runner-up to Johnny Bench for the National League Rookie of the Year honors. The Miracle Mets
 In Koosman posted a 17–9 record with a 2.28 ERA and 180 strikeouts in another All-Star season. That year, he was a member of the Mets team that unexpectedly won the National League East title (both leagues had split into two divisions after expanding from ten teams to 12) after not only finishing dead last in five of their first seven seasons, but also trailing the Chicago Cubs for much of that season by as many as 9 games. After Koosman lost to the Houston Astros to fall to 9–8, he won eight of his final nine decisions. In Game Two of the NLCS against the Atlanta Braves, Koosman was shelled for six runs in 4 innings (including an Aaron three-run homer). The Mets won 11–6, however, then won the next game to complete the series sweep. Koosman was the pitching star of the 1969 World Series against the Baltimore Orioles.