Porter pumped in 21 points and Starks added 16 for the Hoyas (18-4, 8-3 Big East), who caught up with the Golden Eagles for second place in the conference with their sixth straight win.
Both teams remained 1/2-game in back of Big East leader Syracuse.
Nate Lubick also reached double figures for Georgetown with 10 points.
Marquette (17-6, 8-3) turned the ball over 19 times and got a total of nine points out of leading scorers Vander Blue and Davante Gardner in the setback.
Jamil Wilson netted 13 points and Chris Otule added 11 for the Golden Eagles.