The Hornets (32-9) advance to a 3:30 p.m. contest this afternoon versus Randolph-Macon for the right to advance to championship Sunday.
Coleman had reached on a walk and Baker on single to right. The two then moved up 90 feet on a passed ball to set the stage for Arocho to deliver the game-winning hit.
Against a drawn in infield, Arocho laced the single between pitcher Danny Devereux (4-2) and second baseman Chadwick Feeley to complete the comeback.
SU needed the ninth-inning rally as W&L (26-14) had scored one run on three walks and a sacrifice fly against Hornets reliever Phil Morse (4-0) in the top of the frame.
Morse, who came on for starter Darrell Thompson with two outs in the eighth, got out the ninth with a groundout to second.
Thompson allowed three runs (two earned) on six hits and two walks in 7 2/3 innings of work.
Arocho was 2 for 5 with the two RBI.