Yastrzemski enjoyed his best season in 1967, when he won the American League Triple Crown with a .326 batting average, 44 home runs (tied with Harmon Killebrew) and 121 RBIs. Yastrzemski's Triple Crown win in 1967 was the last time a major league hitter won the Batting Triple Crown until Miguel Cabrera in the 2012 season (conversely, six different pitchers have since won the pitchers' version). He was voted Most Valuable Player almost unanimously (one voter chose César Tovar of the Twins). His 12.4 WAR was the highest since Babe Ruth's 1927 season.
1967 was the season of the "Impossible Dream" for the Red Sox (referring to the hit song from the musical Man of La Mancha), who rebounded from a ninth-place finish a year before to win the American League pennant (their first since 1946) on the last day of the season. With the Red Sox battling as part of a four-team pennant race, Yastrzemski hit .513 (23 hits in 44 at-bats) with five home runs and 16 runs batted in over the last two weeks of the season, and finished a mere one game ahead of the Detroit Tigers and Minnesota Twins. The Red Sox went into the final two games of the season trailing the Twins by 1 game and leading the Tigers by 1/2 game. Their final two games were against Minnesota with the pennant and home run title (and hence, the triple crown) on the line. In the Saturday game, Yaz went 3 for 4 with a home run and 4 RBI. Killebrew also homered, but the Red Sox won, 6–4. Thus the teams went into the final game tied for 1st place, and Yaz and Killebrew were tied with 44 home runs apiece. In the final game, neither player homered, but Yaz went 4 for 4 with 2 RBI in the Red Sox' 5–3 win. So in the two games with the pennant on the line, Yastrzemski was 7 for 8 with 6 RBI.