Smithsburg (6-0) pecked away with runs in the third and fourth, including Josh Conway's monster shot to left.
Smithsburg's savvy forced everything to fall apart for South in the bottom of the fifth.
Presgraves' two fielding errors and Taylor Metzger's walk with one out loaded the bases to chase starting pitcher Cory Shank.
Cody Shives welcomed reliever Garrick Boward with a grand slam on a shot to center field for an 8-5 lead.
"(Shives) has been battling for a starting spot and he earned it today," said Cobb. "He wants to be in there."
The Leopards added a run when the Rebels muffed three more plays before Adams ran down a shot in right center, robbing Jack Schwartz of a home run.
"I can't take anything away from Smithsburg, but we beat ourselves again today just like we have all year," said South coach Ralph Stottlemyer. "Can't give a team like Smithsburg six, seven outs in an inning."
To South's credit, it battled back in the sixth against Leopards starter Aaron Schroyer, but he avoided major damage, thanks to an assist from Conway.
Trevor Haupt singled and went to second on a wild pitch for South before Boward singled to center. Conway charged and gunned out Haupt at the plate in a bang-bang play.
But South restarted the rally when Moser drew a walk to set up Jordan Hatfield's three-run homer to cut the deficit to 10-8 and knock Schroyer out of the game.
Nieko Akers closed out the inning and Jay Shafer picked up the save, but not without drama.
Shafer struck out the first two batters before Adams homered. Shafer retired Haupt to end the game.
Presgraves had three of South's seven hits, while Shives added a double for Smithsburg.
Smithsburg 10, South Hagerstown 9
South 005 003 1 -- 9 10 6
Smithsburg 021 151 x -- 10 7 1
Shank, G. Boward (5) and Haupt. Schroyer, Akers (6), Shafer (7) and Gouff. WP -- Schroyer (3-0). LP -- Shank (1-2). S -- Shafer. HR -- SH: Adams 2 (3rd, one on, 7th, none on), Moser (3rd, none on), Hatfield (6th, two on); Sm: Shives (5th, three on), Conway (4th, none on).