Mankato regained a 3-2 advantage after designated hitter Matt Wollenzin's infield single led to an RBI single from catcher Matt Jones.
Bonnell fought out of a jam in the fifth, after two walks and a fielding error by Bonnell loaded the bases with one out. But Dylan Goodwin hit a tailor-made double play to Fuentes to preserve the lead.
"That was the biggest point of the game," Orchard said. "The biggest out of the game. That, to me, could've swung the game either way."
The next time the MoonDogs defense hit the field in the top of the sixth, the lead had ballooned to 12 runs. Mankato added more runs in the sixth and seven innings, capped by solo home runs from Jones and Twichell in the seventh.
Kerwood allowed nine runs in four innings in the loss. Ryan Quick, Zach Hobbs, Trey Higgenbotham and Jesse Harbin all pitched in relief for Mankato. The Border Cats attempted their own comeback in the eighth inning, scoring six runs, including a grand slam from Jacob Rogers.
"Nothing surprises me in baseball," Orchard said. "Every game is different."
After an off-day, the MoonDogs (15-13) continue their homestand Thursday vs. St. Cloud.