1982 – Just five days after hitting three home runs in a 5 – 4 loss to the Twins, California’s Doug DeCinces hits three more home runs in a 9 – 5 win at Seattle, joining Ted Williams as the only American League players ever to hit three home runs in a game twice in the same season.

On August 8, 1982 — 1982 – Just five days after hitting three home runs in a 5 – 4 loss to the Twins, California’s Doug DeCinces hits three more home runs in a 9 – 5 win at Seattle, joining Ted Williams as the only American League players ever to hit three home runs in a game twice in the same season.

Source:
Baseball Reference August 8
National Pastime
Retro Sheet
Hall of Fame
SABR Games Project
Replay The Game