Williams supplied 17 points with seven assists and seven rebounds.
Kris Humphries completed a double-double of 14 points and 21 rebounds as the Nets posted their third win in five games.
Brooklyn broke the game open by hitting 58 percent of its first-quarter shots, including 5-for-8 from long range, to build a 35-17 lead.
Orlando dropped its fourth straight despite double-doubles from Glen Davis (19 points, 10 rebounds) and Nikola Vucevic (14 and 12).
Arron Afflalo contributed 19 points the Magic's effort.