Gaines is leading Roseville Democrat Dennis Campanale 55.4 percent to 44.6 percent with nearly 80 percent of precincts reporting.
The two emerged as the top vote-getters in an eight-way March primary election triggered by her husband Ted Gaines' January election to an overlapping state Senate seat.
Gaines, a marketing consultant for her family insurance business, was considered the front-runner for the runoff contest in the conservative district, which includes Alpine County and parts of Placer, El Dorado and Sacramento counties.
Track the results on the Secretary of State website.
PHOTO CREDIT: Beth Gaines appears at a campaign event at Bass Lake Golf Course in Rescue on April 14, 2011. Autumn Cruz, Sacramento Bee.