Facing the Baltimore Orioles on Wednesday night, Zimmerman hit a solo shot in the first inning, another solo drive in the fourth and a two-run homer in the fifth. All three home runs came off Chris Tillman.
Facing Steve Johnson in the seventh inning, Zimmerman looked at a third strike.
It's the first three-homer game of Zimmerman's career. Earlier in the day, Dioner Navarro hit three home runs for the Chicago Cubs in a win over the White Sox.
The last time two players hit three homers on the same day was Oct. 3 of last year, by Dan Johnson of the Chicago White Sox and Evan Longoria of Tampa Bay according to STATS.
The major league record for home runs in a game is four. The last to do it was Josh Hamilton, for Texas in Baltimore on May 8, 2012.
Zimmerman came in with three homers in 38 games this season. Navarro also began the day with three home runs.