Posey's Giants trailed 2-0 entering the fifth frame during the 3-2 win Sunday at PNC Park in Pittsburgh. Josh Bell's hit a two-run home run in the bottom of the fourth inning to give Pittsburgh the early advantage.
Dereck Rodriguez began the fifth inning with a single to left field. Steven Duggar followed with a bunt for a single, putting runners on first and second base for San Francisco.
Gerardo Parra popped out on a bunt, before Posey stepped to the plate. The veteran catcher worked the count even at 1-1 against Pirates star Chris Archer.
The right-handed starter fired in a 92.5-mph fastball with his third offering of the exchange. Posey pummeled the pitch to center field for a 409-foot bomb. Posey's three-run blast had an exit velocity of 107 mph and a launch angle of 24 degrees, according to Statcast.
The Posey blast ended a streak of 237 at-bats without a home run. His last long-ball came on June 19.
"It obviously felt good," Posey told reporters, according to MLB.com. "I've been trying to just stay positive and know that this is a process. I come to the field each day with an attitude to keep on going. Hopefully, things are where my expectations are at some point."
The Giants snapped a four-game losing streak and stopped the Pirates from completing a series sweep with Sunday's win. San Francisco has another road series against the Toronto Blue Jays on deck. The Blue Jays host the Giants in the first game of the two-game matchup at 7:07 p.m. Tuesday in Toronto.