Porter hit one free throw, which was the only score in the final 2:22 of the game to preserve the win for the Hoyas (14-4, 4-3 Big East), who have won four of their last five games.
Markel Starks also scored 17 for Georgetown. He and Porter were the only players in double figures for the Hoyas, who shot 39.6 percent from the field to 34 percent for Louisville.
Louisville (16-4, 4-3) lost its third consecutive game. Russ Smith, Gorgui Dieng and Luke Hancock each scored 12 for the Cardinals.
Georgetown led 33-29 and held on for the win despite scoring only 20 points in the second half.