Democratic candidate Katie Hobbs has defeated Republican Kari Lake in Arizona's race for governor, CBS News has projected.
The result is a rebuke of Ms Lake, who has peddled the false claim that Donald Trump won the 2020 US election.
In her victory statement, Ms Hobbs said that "in this moment of division" she would work for everyone in the state.
Ms Lake appeared to suggest that the result was incorrect, and that some votes for her had not been counted.
Elsewhere, almost a week after votes were cast, the race to control the House of Representatives remains tight.
Republicans must win at least 218 seats to claim a majority in the House of Representatives, a prospect that has sharply narrowed.
The party has currently won 215 seats while Democrats have won 211, according to race projections from CBS News.
In a midterm election that has further highlighted the stark partisan divisions in America, Ms Hobbs called for unity, saying she would work for those Arizonans who did not vote for her.
"Even in this moment of division, I believe there is so much more that connects us," she said.
Thanking voters on Twitter, she added: "Democracy is worth the wait."
Ms Lake however, struck a more combative tone on social media, tweeting that "Arizonans know BS when they see it".
The candidate – who was endorsed by Mr Trump – told the BBC during campaigning that the former president should not need to run again in the 2024 election because "he won the last election". She predicted he would "come back with a vengeance".
In response to Lake's expected loss, the former president posted on Truth social – a social media platform he founded.
"Wow! They just took the election away from Kari Lake. It's really bad out there!" he wrote.
There is no evidence that the 2020 election was stolen or that this month's Arizona vote was taken away from Ms Lake.
The defeat sees Ms Lake join the ranks of pre-eminent Trump-backed election deniers who lost last week. But a BBC News tally of results found at least 125 election deniers have won races for the House, Senate and governorships.
This video can not be played
BBC's Katty Kay challenges Kari Lake on election claims
The midterm elections are also for Congress, including all seats in the House of Representatives and one third of those in the Senate.
The Biden administration had feared that a loss of power in Congress would bring the president's agenda to a halt. However, the Democrats have retained control of the Senate, and the House has not yet been called.
If the two parties split control of Washington, Democrats will "maintain our positions" but voters should not "expect much of anything", President Biden said on Monday.
Speaking to reporters in Indonesia, where he is attending the G20 summit, Mr Biden said the results had "sent a very strong message around the world that the United States is ready to play" and wants to remain "fully engaged in the world".
He noted there was "a strong rejection" of election denialism, political violence and voter intimidation. But he warned that, without a majority in the House, Democrats would be unable to codify abortion rights through legislation, a key priority for liberal voters.
Out of the 11 House races that still remain to be called, most are in western and southwestern states, including California and Arizona.
Newly elected members of Congress, including the first lawmaker from Generation Z and the first openly gay Republican, have already begun arriving in Washington for orientation.
History suggests the party controlling the White House usually loses seats in a midterm election, and Democrats' performance this year is considered the best for a sitting party in at least 20 years.
That has endangered leadership bids for the top Republicans in the Senate and House ahead of the party's internal elections on Tuesday.
House Minority Leader Kevin McCarthy – who hopes to succeed Nancy Pelosi as Speaker in the next Congress – and Senate Minority Leader Mitch McConnell are both reportedly scrambling to garner support from their colleagues.
Divisions within the party have been on full display in recent days as former President Donald Trump, who has received some of the blame for a poor showing, prepares to launch another presidential run later this week.
Mo Brooks, a Republican representative in Alabama and once a strong supporter of Mr Trump, said it would be a "bad mistake" for the party if the former president was their nominee in 2024.
"Donald Trump has proven himself to be dishonest, disloyal, incompetent, crude and a lot of other things that alienate so many independents and Republicans. Even a candidate who campaigns from his basement can beat him," Mr Brooks told AL.com.
The election-denier who wanted to be Arizona governor
Republican anger over midterm election failings
What Democratic Senate means for Biden and Trump
Iran must heed protesters' demands – ex-president
British peer Mone to take leave of absence from Lords
US Capitol riot panel to make criminal referrals
Billie Eilish: Growing up in public has been bruising
The lives changed by the 2012 Delhi gang rape
Dazzling Brazil dismantle South Korea in last 16
Why is mac and cheese up in court? Take our timed quiz…
The spy, the president and the cash in the sofa
Inside the capital taken hostage by brutal gangs
The radical 'soft girl' trend millennials love
Why have so few elderly Chinese been vaccinated?
Inside the world of South Korean male beauty pageants
Zimbabwe's stunning 80km safari train
The misery of middle managers
The love song that became an anthem
© 2022 BBC. The BBC is not responsible for the content of external sites. Read about our approach to external linking.