The veteran first baseman reached the historic mark when the game was only in the sixth inning. He accounted for 10 of the Pirates' 12 runs in their 12-4 win over the Braves and tallied a career-high 13 total bases.
O'Hearn finished the game going 4-for-5 at the plate, also hitting a single.
O'Hearn is now hitting .293 with an .851 OPS, 16 home runs, and 61 RBI through 77 games. Pittsburgh signed the 32-year-old to a two-year, $29 million contract during the offseason, and he has proven to be a perfect addition.
He's just second to Brandon Lowe in both home runs (21) and RBI (64), second to Nick Gonzales in batting average (.314), and second to Bryan Reynolds in OPS (.870) on the team.
O'Hearn has missed some time this season after landing on the 10-day injured list for a right quadriceps muscle strain back in May, but hasn't lost a single step.
The win marked the third straight for the Pirates, tied with the Miami Marlins and Milwaukee Brewers for the best win streak in the National League, as they improved to 47-45, and 6-4 in their last 10.