Before Bradley's rocket in the seventh, Boston was trailing, 4-0, and Cardinals right-hander Mike Leake was rolling.
One hit by Bradley cut that deficit in half and gave the Red Sox life.
"Jackie with the big two-run home run that got us off from nothing, because Leake was very good," said Red Sox manager John Farrell.
Though Bradley still thinks his two-run shot onto Eutaw Street at Camden Yards on April 22 was his most impressive long ball, the projected distance of 441 feet on Wednesday was his longest in the Statcast™ era, which dates back to 2015.
"It felt good off the bat," said Bradley.
For Bradley, it felt particularly good, because he is starting to emerge from the depths of a prolonged slump.
During the two games in St. Louis, Bradley was 4-for-8 with the two homers and two walks. For the season, he is slashing .212/.377/.388 with four homers and 10 RBIs, a long way from the production he displayed while becoming an All-Star in 2016.
"It feels great," Bradley said of the two games in St. Louis. "I'm going to still continue to work. I'm a work in progress. Obviously I got off to a slow start, so I've got a lot of ground to catch up on."
What Bradley has done the past two games could be a product of the extra cage work he did from May 6-9 when Farrell held him out of the lineup for three straight games.
"I think you trace it back to his ability to hit the ball to left field," Farrell said. "It's allowed him to stay on some pitches. He gets a ball over the middle of the plate and hits it a long way. So to his credit he's worked hard, he's worked long. He's fought a little bit of a downturn and hopefully he's coming out of it."
Ian Browne has covered the Red Sox for MLB.com since 2002. Follow him on Twitter @IanMBrowne and Facebook. This story was not subject to the approval of Major League Baseball or its clubs.