Bour's first-inning grand slam changed everything early.
"I think it energized everyone," Marlins manager Don Mattingly said. "They kind of ambushed us quickly there in the first, getting those six hits. We were lucky to get it up there. It could have been bad."
Tom Koehler was roughed up in the first inning, as the Cubs scored four runs on six straight hits. Kris Bryant and Willson Contreras both homered in the first inning.
Down four before they had an at-bat, the Marlins cashed in on shortstop Addison Russell's error on Derek Dietrich's routine grounder. With two outs, Kyle Hendricks walked Marcell Ozuna and Giancarlo Stanton, loading the bases for Bour.
"Those are some huge at-bats in front of me," Bour said. "I was just fortunate enough to put a good swing on the bat."
Bour took Hendricks deep to center field. The Cubs right-hander knew it immediately, as he dropped his head after seeing the swing.
Statcast™ projected the drive at 436 feet with an exit velocity of 104 mph.
Bour now has 13 home runs, and his 40 RBIs are second on the team to Ozuna's 44. It was Bour's second grand slam of the season, with the other on June 10 at Arizona.
But after the first inning on Friday, the only other hit the Marlins had was Adeiny Hechavarria's single to lead off the seventh.
"You're in a game," Mattingly said. "That's not going to happen very often. We need to do more than that. Tonight was a game we could have [rallied]. We get one hit and get four runs. But from there, we weren't able to muster a whole lot."
Koehler made Bour's slam matter, because he regrouped from the second through sixth innings, allowing one hit and no runs.
"It was kind of like the game starting over there again," Koehler said. "At that point, you want to get as many zeros as you can and keep the team in it. ... They made a defensive mistake early. It turned into four runs. You keep the team within striking distance. With our offense, we're never out of it."