Cuba earned its ticket to the finals after twice coming from behind to defeat Chinese Taipei 7-4 in a rain delayed game on Saturday. At one point Cuba was down 4-1.
The US lost for the first time 8-6 in ten innings to Japan, but already had its slot in the finals guaranteed.
Cuba was led by Orlando Roa Garcia who hit two homers and drove in three runs. Jorge Martinez pitched 5.1 innings of scoreless relief to get the win.
The 2011 IBAF 16U Baseball World Championship is being played in Lagos de Moreno and Aguascalientes, Mexico. The title game starts at 4:00 p.m. local time on Sunday.
The finals rivals are a rematch of the 2009 tournament when the US scored twice in the bottom of the ninth to defeat Cuba 7-6.