Mark McGwire ties a major league record by hitting five home runs in back-to-back games. His three homers today in consecutive at-bats help the Oakland Athletics defeat the Boston Red Sox, 8 – 1.

On May 30, 1995 — Mark McGwire ties a major league record by hitting five home runs in back-to-back games. His three homers today in consecutive at-bats help the Oakland Athletics defeat the Boston Red Sox, 8 – 1.

Source:
Baseball Reference May 30