Lt. Gov. Gavin Newsom cruised to victory in Tuesday's primary and will face former California Republican Party Chairman Ron Nehring in November.
With about half the votes counted, the former San Francisco mayor had 52 percent of the votes while Nehring finished a distant second with about 23 percent.
Nehring, who held the GOP post from 2007 to 2011, easily outdistanced two other Republicans. David Fennell and George Yang each had less than 10 percent.
Nehring is seeking to break the Democrats' monopoly in Sacramento, where they hold all eight statewide offices.