House Speaker Sara Gideon decisively won the Democratic primary for U.S. Senate on Tuesday and will face incumbent Republican Sen. Susan Collins in November in one of the most anticipated races in state history.

The Bangor Daily News and its national election results partner, Decision Desk HQ, called the race at 9:06 p.m., when unofficial results showed Gideon with 73.5 percent of votes. It was well over the 50 percent threshold necessary to avoid a ranked-choice runoff.

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Gideon will now formally go head-to-head with Collins in what is already the most expensive congressional race in Maine’s history. Both candidates are likely to be in the national spotlight as Maine is considered a pivotal state for Republicans looking to hold onto the Senate and Collins has become a target for liberals who argue the senator long seen as a moderate has failed to adequately stand up to President Donald Trump.

Hallowell lobbyist Betsy Sweet, who was backed by some national progressive groups in her insurgent campaign, was heading toward a second-place finish with 21.2 percent of votes while Saco lawyer Bre Kidman had 5.3 percent with 3.8 percent of precincts reporting.

House Speaker and Democratic U.S. Senate candidate Sara Gideon speaks with her staff and the owner of Harvest Moon Deli outside the sandwich shop in downtown Bangor on Election Day. (Natalie Williams | BDN)

Gideon, of Freeport, was considered the favorite going into Election Day, with backing from national Democrats as well as many state legislators. Her campaign has raised an unprecedented $23 million, including $9 million during the second quarter, and she has been the primary target of attacks from the Collins campaign and outside Republican groups.

In an address delivered via Facebook Tuesday night, Gideon said she looked forward to working with Kidman and Sweet, citing their passion and calling Collins part of a “broken system.”

“I see how we can come together and build a better future for everyone,” Gideon said. “We all have the opportunity to help make that happen this November.”

She largely ignored Sweet and Kidman during the campaign to focus on Collins. On health care, Gideon threw her support behind a public option while Sweet, who previously finished third in the 2018 gubernatorial primary, and Kidman, a first-time candidate, favored plans like Medicare for All, backed by progressives including Vermont Sen. Bernie Sanders.

Kimberly Paige, 54, of Bangor, said she voted for Gideon because the Freeport Democrat “seems to have her finger on the pulse of Maine and what Maine needs.” Malcolm Coulter, 76, a teacher from Presque Isle, said Gideon’s experience set her apart from the other candidates.

“She would be the one who would have the best chance of defeating Susan Collins in November,” Coulter said.

Collins is one of national Democrats’ top targets as the party looks to take the U.S. Senate majority back from Republicans. The fourth-term Republican, who won with two-thirds of votes in 2014, angered liberal voters with her 2018 vote to confirm U.S. Supreme Court Justice Brett Kavanaugh, prompting a fundraising spree that raised more than $4 million for her eventual opponent. That money will now be transferred to Gideon.

House Speaker Sara Gideon, D-Freeport, greets news media near a polling station on Tuesday in Portland. (Elise Amendola | AP)

In a Tuesday night statement, Sweet said she looked forward to “working together side by side” with Gideon “to ensure this is Susan Collins’ final term.”

Gideon and Collins will be joined on the November ballot by two independent candidates, former Green party candidate Lisa Savage and conservative businessman Max Linn, although a Collins ally recently challenged Linn’s signature submissions. The general election race will use ranked-choice voting, as did the primary.

BDN writers Eesha Pendharkar and David Marino Jr. contributed to this report.