With 89 percent of the precincts reporting, McAleer had 68.1 percent of the vote to Combe's 31.9 percent.
McAleer's showing was especially strong in Summit County, where she won 90.8 percent of the vote, according to the unofficial tally. She was expected to win her home county easily, but taking 90-plus percent of the vote is an extraordinary feat in a contested campaign.
McAleer advances to the November ballot. She will challenge Congressman Rob Bishop, the Republican incumbent, in a heavily GOP district. A McAleer win on Election Day would be seen as one of the nation's political shockers.
McAleer's background is in management consulting and the nonprofit sector. She was an Army officer.
In the Republican Senate primary, meanwhile, incumbent Orrin Hatch was beating challenger Dan Liljenquist by more than 30 points in the statewide tally with 68 percent of the precincts reporting. Hatch won Summit County by a count of 1,749-880, according to preliminary results.