Ryan Abernathy led the way for St. Joe (2-0) pounding out four of the team's eight hits, two RBI and scoring three runs.
Lucas Powers led off the third with a double, and scored on an extra-base hit from Abernathy to start a three-run frame.
The Mustangs tacked on another run in the fifth before blowing up in the next inning.
St. Joseph's six run sixth came on three walks, two hits, two wild pitches, a sacrifice fly, a fielder's choice and a hit batter.
Nate Winfrey drove in a pair of runs and walked twice in the win, while Powers went 1-3 with a walk and two runs scored.
The Rattlers only runs came after a pair of errors in the fourth.
Mustangs starting pitcher Trent Kinney allowed two unearned runs on three hits and two walks in six innings.
St. Joseph hosts its first doubleheader of the season Thursday night. They play the Spooner Bandits with the first game starting at 5:30pm.