By Tuesday, Matheson captured 119,803 votes to Love's 119,035, according to figures from the four counties.
Love's defeat came as Republicans captured every major Utah race easily, including wins for Gov. Gary Herbert, U.S. Sen. Orrin Hatch and three other congressional seats, as well as four seats in the Utah Legislature that were previously held by Democrats.
But when late Election Day returns showed Matheson eking out a narrow victory, a hush fell over the Republican election night headquarters at the Salt Lake City Hilton. Top party officials refused to concede Love had lost. The candidate herself could only offer Matheson congratulations without actually conceding in a speech to supporters.
Love later said she was "absolutely" stunned by the defeat. She would have become the first black woman elected to Congress as a Republican.
A lot of money was on the line. The candidates waged a $10 million-plus advertising war with help from outside groups. The spending by each side was roughly even in Utah's most expensive congressional race.
"She came out of the gates very strong, but he patiently chipped away at her Republican votes," said Monson, who conducted an exit poll Election Night that showed the race was too close to call.
Love got a boost from her speech in August at the Republican National Convention and appeared to be taking a lead in September polls.
But Matheson was just getting started.
"He chipped away at her, by pointing out a lot of potential red flags about her: Her readiness for the job, and ideological position on some of these issues," Monson said. "In particular, he made inroads with older voters on Medicaid and Social Security."
Republicans had only one person to blame.
"They're calling me a spoiler," said Jim Vein, the Libertarian candidate who captured what for him was a surprising 2.5 percent of the vote— enough to put Love over the top.
"I don't feel like a spoiler. Mia Love didn't run her campaign well," said Vein, 53, of Orem. "She said she didn't anticipate me, and others didn't think I'd make a splash. I've gotten some nasty emails and phone calls saying I ruined a good Republican."