McDaniel, who finished the day 4 for 5, was in position to play the hero as Arens led off the SU (25-7-1) ninth with a single to center, was sacrificed to second and following an intentional walk to Michael Paul, stole third.
Daniel Freshley loaded the bases by drawing a walk off reliever John Woodard, who had come on for Justin Petock (1-1) after Petock gave up the Arens single and the intentional pass to Paul.
McDaniel lined a 1-2 fastball into the gap in left center, allowing Arens to trot home with the winning run.
The hit, the ninth of the game for the Hornets, made a winner of junior Michael Scimanico (6-0).
Scimanico threw a 119-pitch complete game, striking out eight and walking two.
The southpaw allowed just four hits, two of which happened in a three-run Bridgewater (23-13-1) eighth.
The Eagles used two SU errors to score two unearned runs and take a 3-1 lead; Shenandoah answered with two in the bottom of the frame to knot the game at 3-3 heading into the ninth.
Scimanico worked a 1-2-3 ninth, setting the stage for the offense to win it in walkoff fashion.
Designated hitter Nolan Overby had the big hit in the Hornets eighth, plating McDaniel and Freshley with a triple into the right field corner.
McDaniel and Freshley both reached with singles to center off of Petock.
Arens had two hits to back up McDaniel and drove in the Hornets first run of the game with a single to right in the seventh.
The winner of that contest advances to the championship game.