With Boston and Toronto tied at 7 in the ninth inning Thursday night, Hernandez hit a 1-0 pitch from Blue Jays closer Ken Giles to left field. The ball only traveled 348 feet but went over the wall for a late Red Sox lead.
"His swing is so simple," Red Sox manager Alex Cora said. "He stays on pitches. When he's driving the ball the other way, it's a good sign. ... That's a good pitch right there from Kenny and he put a good swing on it. He's a strong kid, big and strong."
Hernandez is hitting .317 with two home runs and seven RBIs in 41 at-bats this season.
Boston trailed 6-1 in the sixth inning. All-Star Mookie Betts walked and the Red Sox recorded three straight singles before rookie Michael Chavis' 15th home run of the year, a three-run shot to left field.
"You know we're down, and it's really easy just to give up or be lackadaisical and let the game go out," Chavis said, "but if you were in our dugout, by the vibe and how guys are talking, we never thought we were out of it."
Boston is 46-41 this season. The Red Sox are 2 1/2 games behind the Cleveland Indians for the American League's second Wild Card spot.