Utahns also cast ballots in three other congressional races, and were deciding a host of statewide offices, including attorney general, state auditor, treasurer and 101 legislative seats.
Republican John Swallow held an early lead over Democratic challenger Dee Smith in the race for Utah Attorney General. Swallow has been chief deputy under current Attorney General Mark Shurtleff, who is retiring, while Smith serves as Weber County attorney.
Two constitutional amendments also were on the ballot.
One initiative would decide whether members of the military should be exempt from property taxes if they serve on active duty out of state at least 200 days a year. They could claim the exemption for their primary residence the year after service was completed.
The second amendment would determine whether some of Utah's severance tax revenue from mining, oil and gas companies should be deposited into a rainy-day fund. State lawmakers then could only spend from the fund's principal in an emergency and with approval from the governor and three-fourths of the state Senate and House.
In other congressional races, Democrat Jay Seegmiller, an Amtrak conductor and former state legislator, faced Republican newcomer Chris Stewart, a former Air Force pilot, environmental consultant and author, for the District 2 seat vacated by Matheson.
Meanwhile, incumbents held solid leads in the two other U.S. House races. In District 1, five-term incumbent Rep. Rob Bishop was favored to win over Democratic political newcomer Donna McAleer, of Park City, the director of a health care nonprofit. In District 3, covering southeast suburbs of Salt Lake City to the Arizona and Colorado borders, U.S. Rep. Jason Chaffetz also was heavily favored to beat Democrat Soren Simonsen, an architect and the chairman of the Salt Lake City Council.