Army Reserve veteran Abe Hamadeh leads venture capitalist Blake Masters in the Republican primary race for Arizona's 8th Congressional District.
Both Hamadeh and Masters were endorsed by former President Donald Trump.
With 75% of the precincts reporting, Hamadeh led Masters with 29.8% of the vote to 25.3%, according to Decision Desk HQ.
They were followed by Arizona state House Speaker Ben Toma (21.3%), former U.S. Rep. Trent Franks (16.6%) and state Rep. Anthony Kern (4.8%).
Arizona, a key swing state that often spurs national debates over abortion and immigration, plays an outsized role in determining control of Congress and the White House. Some political observers consider the 8th District, northwest of Phoenix, the epicenter of efforts by Trump allies to cast doubt on the validity of election results.
Whoever wins has a good chance of succeeding Republican U.S. Rep. Debbie Lesko because the district leans conservative. Greg Whitten, a biosecurity worker, is running unopposed in the Democratic primary.
The Associated Press contributed to this story.