Hillary Clinton defeated her rival Bernie Sanders in Puerto Rico's Democratic primary Sunday, US networks projected, bringing her to the brink of victory in their long-fought battle for the party's presidential nomination.

With 22 percent of the island territory's districts reporting, former secretary of state Clinton was ahead with 64.2 percent of the vote, compared to 35.3 percent for Sanders, according to CNN.

The victory, combined with Clinton's overwhelming win in the US Virgin Islands a day earlier, gives her a big boost ahead of Tuesday's culminating vote with New Jersey and the big prize of California at stake.