On May 10, 1956 — 1956 – At Yankee Stadium, Bob Lemon gives Cleveland a 7 – 2 win over the Yankees. Mickey Mantle has a solo homer in the 6th for New York. By the end of the month, Mantle will have hit his 20th homer and will be batting .425 with 50 RBIs.
Source:
Baseball Reference May 10