Donald John McMahon (January 4, 1930 – July 22, 1987) was an American right-handed relief pitcher in Major League Baseball.

A little more than a month later, when McMahon retired, only Hoyt Wilhelm, Lindy McDaniel, and Cy Young had pitched in more games.

He was activated by San Francisco for parts of the 1972, 1973, and 1974 seasons when the Giants needed his experienced and effective arm to help out in the bullpen.

In 1986, after a recommendation from friend and fellow high school classmate Al Davis, he was hired as a scout for the LA Dodgers.

[2][3] In 1987, he was working as an instructional coach and scout with the Los Angeles Dodgers and often pitched batting practice before many home games.