[4] He managed to improve his batting average to .285 and hit more home runs (7) and RBIs (46) in 136 games, but committed 17 errors and recorded a disappointing .940 fielding percentage.

[4] Mangual made his MLB debut on September 15, 1969, at the age of 22,[1] entering as a pinch hitter and grounding out in his only plate appearance in a 4–3 loss to the Philadelphia Phillies.

[6][7] Mangual spent the entire 1970 season in the minor leagues,[4] having been the final outfielder to be cut from the spring training roster.

[4] He was subsequently traded to the Oakland Athletics on October 20 that same year, as the player to be named later to complete the deal that sent Mudcat Grant to the Pirates one month earlier.

[2] Mangual's performance eventually improved,[2] and he notably hit a walk-off single in the 20th inning against the California Angels on July 9, 1971.

[2] Mangual's strong showing led to him finishing third in the American League (AL) Rookie of the Year balloting,[2] behind Bill Parsons and winner Chris Chambliss.

[1] His defense proved to be unreliable;[2] he made 5 errors and Reggie Jackson ended up playing nearly four times as many games at center field as Mangual.

[1] During Game 4 of the 1972 World Series, Mangual hit a walk-off single in the bottom of the ninth inning against the Cincinnati Reds.

[1] Mangual auctioned his personal replica of the Commissioner's Trophy, given to every A's player on the 1972 team by owner Charlie Finley, in August 2010.

[2] In an interview he gave eight years later, he spoke fondly of his time with the Athletics, crediting the support given to him by teammates like Reggie Jackson, Joe Rudi, and Ray Fosse.