Republican U.S. Senate candidate Dan Sullivan appeared to grab an insurmountable lead over incumbent Democratic Sen. Mark Begich early Wednesday, with all of Alaska's precincts reporting.

With results from all 441 precincts counted, Sullivan led 49 percent to 45 percent. The margin remained essentially the same from the first returns early in the evening.

Speaking just after midnight at his election night party in a packed ballroom at the Hotel Captain Cook, Sullivan praised his supporters and told them: "We are taking back our country!"

"We're still going to be respectful of the process," Sullivan said. But he nonetheless touted Republicans' successes in Senate races across the country Tuesday, and to hearty cheers, he proclaimed that the party had sidelined Harry Reid, the Democratic leader in the Senate.

"We're going to take back America, the land that we love," Sullivan said, as the crowd erupted in chants of "USA! USA!"

Shortly before midnight, Begich's campaign issued a statement saying he wouldn't be commenting on the race until all the rural Alaska precincts were counted.

The Senate race was the costliest campaign in Alaska's history, with more than $50 million spent by the two major candidates and the groups that supported them. The race was viewed as potentially pivotal in flipping control of the Senate out of the hands of Democrats.

But by the time polls closed in Alaska, control of the Senate was already decided, with Republicans winning key races in Colorado, Arkansas, North Carolina and Iowa. And as they awaited results, Sullivan supporters at his party joked they were expecting the arrival of a Republican "red bore tide" in Alaska.

"We saw a wave today," said Sullivan's political consultant, Mike Dubke.

With votes from some precincts still uncounted early Wednesday, Sullivan's campaign hadn't officially declared victory.

Tens of thousands of additional votes won't be counted until next week, at the earliest, state election officials said. That includes some 20,000 absentee votes the state hadn't counted as of Tuesday evening -- and even more absentee ballots will continue to arrive through a Nov. 19 deadline. There are also an unspecified number of so-called "questioned ballots" -- typically cast by people who voted at the wrong polling place -- of which there were approximately 13,000 in the last midterm election, in 2010.

But Democrats would need a huge advantage among those uncounted voters to close Sullivan's lead, which sat above 8,000 votes.

Begich left his party, at a downtown pizzeria, without speaking to media, and several outlets reported he would not concede election night.

A statement from his campaign shortly before midnight said: "Sen. Begich is proud to have run the most extensive campaign in rural Alaska's history and to have stood for the rights of Alaska Natives and rural Alaska. Begich will make a statement on the race after counts arrive from the 70 outstanding villages," and when the number of outstanding ballots is clear.

Speaking to supporters earlier, Begich compared the evening to his successful bid for Senate in 2008, when he won by 4,000 votes despite trailing by 3,000 on election night.

"I tell people, it's never over until the last counts of the last votes, and that includes bush Alaska," Begich said.

In an interview, however, his wife, Deborah Bonito, acknowledge the wide margin between Begich and Sullivan.

"Oh, I think it's looking really tough," Bonito said. But, she added: "It always looks that way."

As voting began Tuesday, however, Sullivan was the favorite. He'd led in nearly all the pre-election polls, and Republicans outnumber Democrats in Alaska by a 2-to-1 margin -- though there are more independent and unaffiliated voters than people in both parties combined.

Begich, a former Anchorage mayor, won his seat in 2008 just one week after the long-serving incumbent, Republican Ted Stevens, was convicted of federal corruption charges that were later invalidated. On Tuesday, Begich was seeking to win his fourth straight campaign, a string dating back to his first successful bid for mayor in 2003.

Backed by an $11 million ad campaign funded primarily by a Washington, D.C.-based Democratic super PAC, and by a seven-figure ground game investment by the national Democratic Party, Begich was aiming to prove that his election in 2008 was more than a fluke, and that Alaska could elect a Democrat on his own merits.

The Democrats emphasized instances when Begich said he's bucked President Barack Obama, and his shared positions with Republican Sen. Lisa Murkowski. They also touted Begich's knowledge of Alaska issues, his friendly positions to Alaska Natives, to seniors and to pro-choice women, and they tried to tag Sullivan, who was raised in Ohio, as an evasive outsider backed by big-moneyed interests.

Stephanie Simon, 51, a stay-at-home mom who was voting in East Anchorage, said Tuesday she voted for Begich even though she's a Republican.

"He really does work across party lines," she said, adding that Begich and his wife are "very earnest about what they're trying to do for Alaska."

Henry Watson, a 34-year-old African-American from Anchorage who early-voted for Begich last week, said he chose the Democrat because "he's more for minorities."

"He comes to our functions, and he has a voice," Watson said outside his Midtown Anchorage polling place. "He doesn't show up just for us to see his face."

Sullivan is a former state attorney general and natural resources commissioner who served in the U.S. Department of State under President George W. Bush. His campaign stuck to general themes like energy security and federal overreach, while joining with big-spending independent Republican groups to link Begich to Obama's unpopularity in Alaska, and to the president's signature health care bill, the Affordable Care Act.

Mike Hinshaw, 65, said Tuesday he picked Sullivan because Begich is "just in lockstep with Obama."

"And that's sad for America," added Hinshaw, who was voting in East Anchorage and who said he's an independent. Begich has been under the thumb of Reid, the Democratic Senate leader, Hinshaw added, adding that Democrats only allow Begich to vote against his party "to make himself look good."

An early voter for Sullivan, Sherrie Walker, 57, of Eagle River said she was "not sold" on the Republican, adding that "he hasn't addressed" the attacks on his campaign's funders, and on his residency history.

"But it's better than the Big Itch," she said, using her nickname for Begich.

Several voters said they'd been frustrated by the flood of negative campaign ads on television and radio this year – ads backed by the more than $50 million that came primarily from the independent groups, which were newly empowered by a 2010 U.S. Supreme Court ruling that invalidated limits on political spending from unions and corporations.

"I was just disgusted by all the negative ads," said Scott Hines, a 55-year-old Anchorage hospital worker who voted early.

David Breen, 25, also said he was frustrated by the negative tone. But he added that it didn't affect his vote.

"Both candidates were really dirty this election," Breen said. "That made that issue moot for me."

Reporter Tegan Hanlon contributed to this story.