Petrocelli was signed by the Boston Red Sox as an amateur
free agent in July 1961.
Minor leagues Petrocelli spent the 1962 season with Boston's Class B
farm team, the
Winston-Salem Red Sox,
batting .277 with 17
home runs and 80
RBIs in 137 games played. In 1963, he played for the
Double-A Reading Red Sox, again playing 137 games, with 19 home runs and 78 RBIs with a .239 average. Petrocelli was a
September call-up with Boston in 1963, playing a single MLB game, on September 21 against the
Minnesota Twins. He was the starting shortstop and was 1-for-4 at the plate, with his first major league hit being a
double off of
Lee Stange. In 1964, Petrocelli played 134 games for the
Triple-A Seattle Rainiers, batting .231 with 10 home runs and 48 RBIs.
Boston Red Sox ,
Dalton Jones,
Dick Williams and
Dick O'Connell with
Mayor of Boston John F. Collins (at right) in October 1967. Petrocelli spent all of the 1965 season with Boston, playing in 103 games and making 93 starts at shortstop. Early in his
rookie campaign, he experimented with
switch hitting, but after batting only .174 with no home runs through 20 games, he returned to his exclusively right-handed stroke on June 6. For the season, he batted .232 with 13 home runs and 33 RBIs. In 1966, Petrocelli batted .238 with 18 home runs and 59 RBIs in 139 games played. In 1967, Boston's "
Impossible Dream" year, Petrocelli was selected to the
All-Star game; he was the starting shortstop for the
American League team, and went hitless in his one
at bat. Petrocelli played in 142 regular season games, with 17 home runs, 66 RBIs, and a .259 average. In the
1967 World Series, he started all seven games, batting 4-for-20 (.200) with two home runs and three RBIs. Both of his home runs came in Game 6, off of
Dick Hughes of the
St. Louis Cardinals. Boston ultimately lost the series, four games to three. In 1968, Petrocelli played 123 games while batting .234 with 12 home runs and 46 RBIs. In 1969, he set a record (since broken) for home runs by a shortstop with 40; he had 97 RBIs and a career-high .297 average while playing 154 games. He also played in his second
All-Star game, starting at shortstop for the American League squad and going 1-for-3 at the plate, with a double off of
Jerry Koosman. Petrocelli led American League shortstops in
fielding percentage in both 1968 and 1969, at .978 and .981, respectively. Petrocelli hit 29 home runs and had a career-high 103 RBIs in 1970, while batting .261 in 157 games. In 1971, the Red Sox acquired shortstop
Luis Aparicio and Petrocelli moved to third base. He led American League third basemen in fielding percentage (.976), making only 11
errors in 463
total chances. He batted .251 in a career-high 158 games, with 28 home runs and 89 RBIs. In 1972, Petrocelli batted .240 with 15 home runs and 75 RBIs, while playing in 147 games. In 1973, Petrocelli did not play after August 11 due to a
calcium deposit in his right elbow, which required surgery. For the season, he appeared in 100 games, batting .244 with 13 home runs and 45 RBIs. He returned in 1974 to play 129 games with 15 home runs, 76 RBIs, and a .267 average. He did not play after September 15, when he was hit in the head by a pitch from
Jim Slaton of the
Milwaukee Brewers. During the 1975 regular season, Petrocelli batted .239 in 115 games, with seven home runs and 59 RBIs. He missed the second half of August due to an
inner ear problem, likely related to his 1974 beaning. Boston won the
American League East, and faced the
Oakland Athletics in the
American League Championship Series. Petrocelli started all three games at third base, as the Red Sox swept the A's, while batting 2-for-12 (.167) with a home run and two RBIs. In the
1975 World Series, which Boston lost to the
Cincinnati Reds, Petrocelli hit .308 (8-for-26) with four RBIs, starting all seven games at third base. He did not commit an error during the 1975 postseason. In 1976, Petrocelli was placed on the
disabled list on August 20, due to further inner ear problems; he played in only three more games that year. For the season, he batted a career-low .213 with three home runs and 24 RBIs in 85 games played. Supplanted by
Butch Hobson as the team's regular third baseman, Petrocelli was released by the Red Sox during
spring training on March 26, 1977. During his career with the Red Sox, Petrocelli hit 210 home runs with 773 RBIs and 653 runs scored in 1553 games played, with a .251 average. As of 2018, Petrocelli holds MLB's eighth-best all-time fielding percentage for third basemen (.970). He was inducted to the
Boston Red Sox Hall of Fame in 1997. ==Post-playing career==