Stanford's Teresa Noyola and Florida State's Tiffany McCarty also scored for the Americans, favored to clinch one of the three Concacaf berths at the Under-20 Women's World Cup later this year.
The USA dominated Jamaica with a 21-3 edge in shots.
Leroux had an eventful first half, hitting the woodwork twice, and scoring both her goals. The UCLA sophomore also had an assist on Noyola's goal.
Jamaica's best chance came in the 24th minute when Sashana Campbell blasted a free kick off the crossbar
"It was a fantastic start to the tournament," said U.S. coach Jill Ellis. "There were some good goals and I was happy that we didn't concede any. I thought there was a little anxiety, but we settled the game pretty quickly."
The other three opening matches were all one-goal games: Canada-Costa Rica 1-0, Guatemala-Cuba 2-1 and Mexico-Trinidad & Tobago 2-1.
Jan. 21 in Guatemala City
USA 6 Jamaica 0
USA - Nairn (McCarty) 9th
USA - Leroux 25th
USA - Leroux (Henninger) 35th
USA - Noyola (Leroux) 49th
USA - Nairn 72nd
USA - McCarty (Bywaters) 83rd
USA -- Henninger, Quon, Dunn, Pressley (Brooks, 75), DiMartino, Bywaters, Richmond, Nairn, Noyola (K.Mewis, 57), Leroux (Hayes, 62), McCarty.
Jamaica -- Spence, Blake, Hyre, Small (Rose, 56), Honegan, Foster (Dobson), Clarke (Thomas, 61), Campbell, Rogers, Pryce, Campbell.
Referee: Erika Vargas (Costa Rica).