Deirdre Demet-Barry of the United States took the silver on the 24-km route along the Aegean coastline while Karin Thuerig of Switzerland took bronze.
Zijlaard-van Moorsel's emphatic victory came just three days after she fell in the women's road race, injuring her head, hip and shoulders.
France's 45-year-old Jeannie Longo finished nearly two minutes off the pace in what may be the last race of a remarkable Olympic career which started at the Los Angeles Games in 1984.