Benally gained 521 votes to defeat Roger Atcitty, who was the choice of 451 voters. She moves on to face Republican Manuel Morgan in the November general election.
More than 1,000 voters cast their ballot is what is the first San Juan County election to be held entirely through mail-in ballots.
County officials are thrilled with voter participation, which exceeds 50 percent of eligible voters.
The participation rate more than doubles voter participation in the 2010 primary election in the district.