Sanders, a self-proclaimed democratic socialist from the US state of Vermont had 53 percent of the vote and Clinton trailed more than six percentage points behind him with 46 percent.
The trend came as a surprise since Clinton had won the previous six primary races against Sanders across northeastern US states by wide margins of usually 20 to 25 percent.
Clinton has a massive lead over Sanders in the number of major contests she has won, in the number of total votes and in the number of pledged delegates supporting her at the Democratic National Convention to be held in the city of Philadelphia in July.
However, Sanders remains popular with his own supporters and continues to receive millions of dollars in small contributions from them, allowing him to carry on the contest to the California primary on June 7.
