The win for the 13th-ranked U.S. team clinched a spot in the London Olympic Games next summer. Argentina, which won last year's world title, was undefeated in Pan Am play since 1987, when the sport was first included.
O'Donnell, the 2010-11 Atlantic Coast Conference Female Athlete of the Year, scored as time expired in the first half to give the Americans a 3-1 lead.
"We have made history today by getting a bid to the Olympics," O'Donnell said. "I don't think anyone on this field thought that we would ever lose this match, and that was the most important thing we had going for us. We had so much trust in each other and knew we would come out on top."