Cougars center fielder Morgan Phillips had a walk-off single that brought home catcher Erven Roper with the winning run in game that lasted 6 hours, 3 minutes.
The game ended two innings short of the NCAA record set when Texas outlasted Boston College 3-2 in the 2009 NCAA tournament. In 1971, Louisiana-Lafayette defeated McNeese State 6-5 in 23 innings.
Charleston tied the game at one in the seventh, then the teams went scoreless the next 12 innings. William & Mary took a 2-1 lead in the 20th before the Cougars tied it once more in their at bat.
Reliever Eric Bauer pitched 10 innings of five-hit ball for the victory.