Freshman Rep. Ann Kirkpatrick (D-Ariz.) will face dentist Paul Gosar (R) in November.
Gosar had been the frontrunner to clinch the nomination after receiving endorsements from several prominent conservatives. He got the backing of Sarah Palin, and in Arizona, he received support from sheriffs Joe Arpaio and Paul Babeu, who also endorsed Sen. John McCain (R-Ariz.).
But mining lobbyist Sydney Hay, who was the 2008 GOP nominee, had more cash on hand in the final stretch of the race. Hay reported $111,000 banked in her last campaign finance report, compared to only $41,000 for Gosar.
Still, Gosar was able to capture 31 percent of the vote; Hay took 23 percent. The rest of the 10-person field, which also included cardiologist Steve Mehta, who was endorsed by the Arizona Republic, former state Senate Majority Leader Rusty Bowers and attorney Bradley Beauchamp, split the remainder of the vote.
The Associated Press declared Gosar the winner with the majority of precincts reporting.