Change is coming to the Virginia House of Delegates’ 33rd District.

For two decades, Del. Joe T. May, a moderate Republican and chairman of the House Transportation Committee, has represented voters across a broad district that spans much of Loudoun County and parts of Clarke and Frederick counties. But on Tuesday, May’s Republican challenger, political newcomer David LaRock, unseated the veteran in a decisive upset, securing 57 percent of the vote in a low-turnout primary election.

It was an unexpected outcome for many in the district, including the winning candidate.

“You hear rumors of polls and surveys, but it was very much a surprise,” LaRock said. “Obviously, a very pleasant surprise.”

In a statement late Tuesday on his campaign’s Facebook page, May, a delegate since 1994, thanked his supporters and expressed regret that he had not secured his 11th term.

“While I wish that the election had turned out differently, it did not,” May wrote. “While we gave it our best effort, it just wasn’t enough. I genuinely appreciate all that each of you have contributed to my experience serving the 33rd District and on my campaigns over the years.”

The race between May and LaRock grew increasingly heated in its final weeks, with the candidates launching pointed attacks against each other. LaRock said May was too moderate on gun rights and abortion, and he assailed May’s support of a landmark transportation funding bill that would raise tax rates. May accused his opponent of lacking strong ideas and common sense, and he distributed campaign mailers citing LaRock’s “arrest record,” a reference to a July 2012 incident in which LaRock removed a sign advertising an adult entertainment store from a fence on private property. LaRock signed an arrest warrant acknowledging the misdemeanor charge, according to court records.

LaRock said he thinks May’s support of the transportation funding legislation passed this year by the General Assembly was a critical point for many voters. The $3.5 billion measure will fund transportation projects and maintenance by raising sales tax rates and adding a wholesale tax on motor fuels.

“People were pretty much unanimously opposed to it,” LaRock said, adding that voters “didn’t oppose appropriating money to transportation, but increasing taxes as opposed to reapportioning money or cutting spending was what people disagreed with.”

Gun control might also have been a deciding factor, LaRock said. May, who said he owns five guns, said he favored “common sense” regulations for how they are used and carried. LaRock said he would oppose further restrictions.

“I really think there’s a strong support for Second Amendment rights among people in the district,” LaRock said in an interview. Many voters “asked me to reassure them that I would stand up for Second Amendment rights” and indicated that it was a key issue for them, he added.

LaRock said his campaign team would take a brief pause to celebrate the primary victory but would then regroup to focus on the general election.

“A primary is very focused on an established group of people who historically vote in that election,” he said. “We’ll reform our strategy around a broader approach, and there will be a more unified effort with the other Republicans who are now at liberty to endorse my candidacy.”

If LaRock repeats his victory in November, 33rd District residents should expect a renewed focus on fiscal discipline: Virginia does not have a revenue problem, but a spending problem, he said.

“There’s just too much money that’s being thrown around without establishing what the spending will achieve,” LaRock said. “Especially in the area of transportation, but also education. In any field, I would like to look at the spending and make sure that it’s being spent well.”

Although there was no Democratic primary contest in the 33rd District, LaRock will not run unopposed in the November, local Democratic officials said. The Loudoun County Democratic Committee announced June 7 that Kathee Myers would run as the Democratic nominee against the winner of the GOP primary.

But on Friday, Loudoun Democratic Committee Chairman Evan Macbeth said it was not certain Myers would continue her campaign. But voters should still expect to see a Democrat in the general election race, Macbeth said.

“Political parties have the right to replace candidates up to 60 days before the election,” he said. “Were Kathee to withdraw from the race, the Democratic Party is confident that we would have a candidate to fight for the votes of the 33rd in November.”

That Democratic nominee is likely to be Berryville lawyer Mary Daniel, who said Friday that she decided to run for the seat after LaRock won the primary.

Daniel, a self-identified moderate Democrat who is president and managing attorney of the Daniel Group, a Winchester law firm, said she had filed for candidacy with the Virginia state board of elections.

“It’s my opinion that Joe May was a great public servant. He did great work, and he was punished by a small group of people for reaching across the aisle and solving a major problem,” Daniel said, referring to May’s support of the transportation bill. “I couldn’t sit idly by . . . I would hope that, like Joe May, I would be able to represent all of my constituents, including independents and Republicans.”