In 1955, he appeared in 22 games for Philadelphia, making only one start, and was winless in two decisions. He did, however, earn his only MLB save that year when he preserved a 10–8 victory over the Cardinals on June 21. The 1955 campaign was Mrozinski's only full year and his last season on a big-league roster. In his 37 games and 821⁄3 innings pitched, he allowed 87 hits and 44 bases on balls; he also struck out 44. Returning to the minors in 1957, he racked up four more years with double-digit victories, and won 119 games overall before retiring from the game.
^Staff. "Ron Mrozinski, Former Philadelphia Phillies Pitcher", Warren Reporter, November 4, 2005. Accessed October 22, 2015. "Ronald Frank Mrozinski, 75, of Washington, beloved husband, father, grandfather and friend, died Wednesday, Oct. 19, 2005 in his home with his family by his side."