Bradley Beal had 21 to lead Washington, which is 1-3 in the preseason.
New York, which has split four games in the preseason, outscored the Wizards 12-2 in the first seven minutes of the second on its way to a 30-16 quarter. The Knicks led 59-46 at halftime.
Washington began the third quarter with a 16-2 run to take a 62-61 lead with seven minutes to play, but New York answered with a 17-6 spurt to lead 78-68 after three.
New York guard Iman Shumpert sprained his right elbow late in the first quarter when he got tangled up with Beal.