St. Joe (5-0, 1-0 MINK) and Joplin were tied 1-1 with two out in the fourth when Abernathy stepped to the plate with two runners in scoring position.
The former Northwest Bearcat tried to check his swing on an 0-1 pitch, but hit a squibber between the mound and first base. Abernathy hustled down the line for a hit and Brady Anderson scored from third to give the Mustangs a lead.
The hit was Abernathy's only one of the game. Anderson, Zac Johnson and Josh Cassidy rounded out St. Joe's four hits in the contest.
Kyle Gehrs picked up the win in his first start of the summer. The former Central Missouri Mule allowed an unearned run in six innings on the mound while striking out four.
Austin Aspegren tossed a scoreless seventh and eighth innings, and Brett Ash closed the door in the ninth for his third save in as many chances.
St. Joseph used a two-out rally in the first inning to open the scoring. Joe Koerper reached on a walk, stole second, then came home on a Johnson's line drive single into center field.
The Mustangs run of seven games in six days continues Saturday at Phil Welch Stadium against the Nevada Griffons.