Lt. Gov. Burt Jones will face off against Rick Jackson, a billionaire health care executive, in a runoff for the Republican nomination to be Georgia’s next governor, according to preliminary results from The Associated Press.

The runoff promises to drag out what has already been a bruising — and very expensive — primary campaign between the two Republican finalists. Mr. Jackson had been largely unknown before pouring millions of his own dollars into an upstart campaign.

The race was initially poised to be a three-way contest between Mr. Jones; Chris Carr, the attorney general; and Brad Raffensperger, the secretary of state. And it looked like it would be a continuation of a philosophical debate that has gripped Georgia Republicans since President Trump lost in 2020, and some of the state’s Republican leaders stood up to his efforts to overturn the result.

Mr. Jones was involved in Mr. Trump’s scheme to change the outcome; Mr. Raffensperger and Mr. Carr challenged the president and were initially rewarded by Republican voters statewide for their defiance, as they — along with Mr. Kemp — fended off primary challengers blessed by Mr. Trump.

Mr. Jackson entered the governor’s race in February. A newcomer with virtually no name recognition, he leveraged his vast wealth to fill the airwaves with ads telling his rags-to-riches story of rising from poverty and foster care to build a business empire. He also benefited from a parallel ad blitz, funded by a mysterious group that did not divulge its benefactors, that relentlessly attacked Mr. Jones, claiming he had used the power of his office to enrich himself and his family.

Mr. Jones repeatedly denied the ads’ claims and accused Mr. Jackson of secretly financing the campaign, which Mr. Jackson denies.

Mr. Jackson eclipsed Mr. Carr and Mr. Raffensperger and caught up to Mr. Jones in the polls heading into Tuesday, a result that voters affirmed at the ballot box.