Porter sank three of the 10 Georgetown (10-1) 3-pointers and notched three assists.
Greg Whittington scored 13 points for the Hoyas, who won their seventh consecutive game.
Whittington, Markel Starks and Jabril Trawick each hit a 3-point shot as part of an 11-point Georgetown run to close out the first half and stake Georgetown to a 40-25 lead at the break.
Daniel Munoz scored 15 points to lead American (4-8), which has lost seven of its last nine games. Stephen Lumpkins added 10 points to the cause, but American shot a tepid 28.6 percent from the field.