One act of selflessness by Bobby Murcer in 1983 led to two legendary careers with the Yankees.

His decision to retire as a player during the season led him to a great career as a broadcaster and allowed Don Mattingly’s major-league career to take off.

“I’ve always felt attached to Bobby [because of that],” Mattingly said yesterday at the All-Star Game FanFest at the Jacob K. Javits Convention Center. “He told me the story of when Mr. Steinbrenner had offered him that [broadcasting] job. They told him they had a guy doing well down [in the minors] and wanted to bring him up, and thought it’d be a great move to move him to the broadcast booth.

“He actually told me, ‘I think it was one of the best things I ever did because it gave me another whole career.’ ”

It gave Mattingly a career, too. The six-time All-Star and 1985 AL MVP for the Yankees is set to take over as the Dodgers’ hitting instructor following the All-Star break. He will reunite with Joe Torre in an attempt to get the Dodgers, who are in second place in the NL West with 46-49 record, into the playoffs.

Mattingly, 47, will try to jump-start an offense that ranked 27th in the majors in runs scored.

“I haven’t looked at all their numbers yet,” Mattingly said. “But they haven’t scored the runs consistently. They’ve got great pitching, but you’ve got to be able to put an offensive attack together every night.”

Working with the Dodgers, who rely heavily on youngsters like Matt Kemp, James Loney and Andre Ethier, will be a change for Mattingly compared to the veteran-laden Yankees squad he worked with previously.

“Yeah, it’s different,” said Mattingly, who signed 500 copies of his book, “Hitting is Simple: The ABC’s of Batting .300.”

“With the older guys like Jeff Kent and Nomar Garciaparra, they know what they want to do. They have their routine and they’re a lot like the Yankees because they have an idea what they want to do with pitchers.

“The younger guys, their swings are good, but it’s about trying to set some good habits with work, with their approach – How are we going to attack this pitcher? – You have to have an understanding of what [a pitcher] is trying to do out there. You can’t just go up there and see the ball and try to hit it.”

dtomasino@nypost.com