Mark Kelly, Democratic candidate for U.S. Senate, speaks during an Election Night gathering at Hotel Congress in downtown Tucson, Ariz. on November 3, 2020.

 Mamta Popat / Arizona Daily Star

Arizona is poised to send two Democrats to the U.S. Senate for the first time in 67 years.

At just before 1 a.m. Wednesday morning, the Associated Press declared former combat pilot and astronaut Mark Kelly as the winner over incumbent Republican Sen. Martha McSally in the race to finish the final term of the late John McCain.

Kelly was leading with 53.4% of the more than 2.6 million votes counted when AP called the race, according to the Arizona Secretary of State's website.

The closely watched and historically expensive Arizona race was expected to help decide which party controls the U.S. Senate, but Democrats' hopes of flipping the chamber were fading Wednesday.

Kelly and McSally were vying for the right to serve out McCain’s last term, which runs through January 2023.

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Gov. Doug Ducey appointed McSally to the seat after McCain’s death in 2018.

At just before 10 p.m., with the result still in question, Kelly addressed supporters at Hotel Congress in downtown Tucson, the same spot where he launched his campaign in February 2019.

Candidates for U.S. Senate, Arizona: Mark Kelly, left, and Martha McSally

It sounded like a victory speech, though he stopped just short of declaring victory.

β€œI’m confident that when the votes are counted we’re going to be successful in this mission,” Kelly said. β€œThis is not about celebrating. This is about getting to work.”

He went on to thank his wife, former Congresswoman Gabby Giffords, his daughters and his twin brother and fellow astronaut, Scott Kelly. He also thanked campaign staff, volunteers, supporters and donors, before launching into a stump speech of sorts that lasted about 15 minutes.

Mark Kelly, right, Arizona Democratic candidate for U.S. Senate, waves to supporters along with his wife Gabrielle Giffords, second from right, and daughters, Claire Kelly, left, and Claudia Kelly, second from left, during an election night event Tuesday, Nov. 3, 2020 in Tucson.

McSally campaign spokeswoman Caroline Anderegg pushed back on AP's decision to call the race in a statement issued at 1:27 a.m. Wednesday.Β 

β€œHundreds of thousands of votes have still not been counted," Anderegg said. "Every Arizonan deserves to have their voice heard and vote counted. We continue to monitor returns. The voters of Arizona decide this election, not media outlets.”

If AP's projection holds up, Kelly could join fellow Democrat Kyrsten Sinema in the Senate before the end of the year, under federal rules that call for a mid-term election winner to be seated as soon as the election results are certified in Arizona on Nov. 30.

McSally, meanwhile, will have lost to both Arizona senatorsΒ β€” first to Sinema in 2018 and now to Kelly.

Sinema congratulated Kelly and took a veiled swipe at McSally in a written statement she issued just after 8 a.m. Wednesday.

β€œContinuing a long tradition, Arizonans again chose independent leadership in electing our new U.S. Senator,” Sinema said. β€œI congratulate Mark on his victory and on the campaign he ranΒ β€” a campaign focused on the issues that matter to Arizonans and how to get results for our state, rejecting the petty politics of name-calling and false personal attacks.”

Sinema said she looks forward to partnering with Kelly to β€œcut through Washington dysfunction." She finished by thanking McSally β€œfor her service.”

This will mark just the fourth time since statehood β€” and the first time since Barry Goldwater replaced Ernest McFarland in 1953 β€” that both of Arizona’s senators have been Democrats.

Kelly led McSally in the polls and in fundraising throughout the campaign, though neither candidate struggled to bring in donations.

The two candidates from Tucson consistently ranked among the nation’s top fundraisers, resulting in what easily ranks as the most expensive political campaign in Arizona history.

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The previous record holder was the McSally-Sinema race in 2018, which saw the two candidates combined to spend about $45 million.

This time around, McSally spent $47.6 million all by herself, while Kelly burned through an eye-popping $77.9 million, according to the nonpartisan Center for Responsive Politics.

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Their combined total of $125.5 million was second highest in the nation behind the $164 million spent in South Carolina by Republican Sen. Lindsey Graham and Democratic challenger Jaime Harrison.

And that doesn’t even count the tens of millions of dollars in outside money that poured into Arizona, as partisan groups wrestled for majority control of the Senate.

With her apparent defeat, McSally has made some unwelcome Arizona history, becoming the first major-party candidate to run for and lose both of the state’s U.S. Senate seats in back-to-back elections.

As it turns out, she may have been bucking the odds from the start. According to the national political website FiveThirtyEight, McSally was the just 12th Republican or Democrat since 1984 to run in a general election for Senate two years after losing in one. Only four of those candidates were victorious on the second try.

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Contact reporter Henry Brean at hbrean@tucson.com or 573-4283. On Twitter: @RefriedBrean