With the win, George Washington climbs back to .500 at 3-3, while James Madison drops to just 1-5 on the season.
Though Larsen and McDonald led the balanced attack, Lasan Komah also scored in double figures with 10 points, and Patricio Garino added nine of his own.
George Washington won despite scoring just five points off the bench.
Andre Nation led James Madison with 19 points and was the only Duke in double figures. Nation also added five steals, four blocks, three assists and four rebounds to round out an impressive stat line.
The Colonials outrebounded the Dukes, 40-28.
The two teams went into halftime tied at 24 and stayed close throughout the second half. In fact, it was not until Garino hit a three with 2:09 left that either team took more than a three-point advantage in the final stanza. That shot put George Washington up by four, and the Colonials would hold on, despite a last-second three from Nation.