(CNN) -- Oregon Democrat Jeff Merkley declared victory over Republican incumbent Sen. Gordon Smith, moving Democrats one seat closer to a filibuster-proof majority in the U.S. Senate.
"This is the beginning of a transformational change for America," Merkley said at a news conference at Portland State University.
He said he would be working with President-elect Barack Obama "to put this nation back on track."
Merkley said Smith called him to concede Thursday morning.
"I thanked him for his 12 years of service to our beautiful state," Merkley said.
Smith had served two terms in the Senate.
"As we exit the stage, our hearts are filled with gratitude," Smith told reporters Thursday evening during a sometimes tearful concession speech.
Smith said he lost because he was swept up in an "Obama tsunami" or a "strong wave" of national Democratic support.
With 92 percent of the ballots received counted, Merkley has received 48.79 percent of the vote to Smith's 45.71 percent, according to unofficial results tabulated by the Oregon secretary of state's office. A third candidate, David Brownlow, has receive 5 percent of the vote.
The as-yet-uncertified vote totals are 796,644 for Merkley and 746,267 for Smith, the secretary of state's office said.
Merkley, the current speaker of the Oregon House of Representatives, joins Democrat Sen. Ron Wyden, who introduced Merkley on Thursday, in Oregon's delegation in the nation's capital.
But even with Merkley's victory, Democrats' hopes are fading for a filibuster-proof 60 seats in the Senate.
Three hotly contested Senate races hang in the balance: Alaska, Georgia and Minnesota.
Democrats needed to add nine seats to their current caucus of 51 (49 Democrats and two independents allied with them) to gain enough of a majority to push legislation through the Senate unimpeded.
It takes 60 votes to invoke cloture, a device to end filibusters, the unlimited floor speeches by an opponent that can prevent legislation from coming up for a vote.
With Merkley's victory, and having added five seats Tuesday, Democrats would need to sweep the three remaining undecided races to reach 60. See a map of the Senate results »
A wild card in the Senate head count is Connecticut Sen. Joe Lieberman, an independent who has caucused with the Democrats but who was an ardent supporter of Republican presidential nominee Sen. John McCain. If Lieberman switches his allegiance to the GOP, the Democrats cannot reach 60, and the filibuster remains in play.
A recount is expected in the tight U.S. Senate race in Minnesota, but GOP incumbent Norm Coleman claimed victory anyway Wednesday, despite leading Democrat Al Franken by only a few hundred votes.
"I recognize that because of my margin of victory, Mr. Franken has the right to pursue an official review of the election results. It is up to him whether such a step is worth the tax dollars it would take to conduct," Coleman said.
"Yesterday, voters spoke. We prevailed," he added.
With all of the precincts reporting, Coleman and Franken were separated by about 720 votes Wednesday afternoon, and the Minnesota secretary of state's office said a recount probably would be held.
"From what it looks like, that's where it's headed," said John Aiken, the secretary of state's director of communications.
According to the figures, posted on the secretary of state's Web site, Coleman received 1,211,616 votes, or 42 percent, and Franken garnered 1,210,895 votes, or 41.97 percent. The vote count kept changing slightly as more counties reported their results.
Recounts are triggered in Minnesota when the winning margin is less than half of 1 percent.
"One half of one percent is 15,000 votes," Aiken said. "We are looking at a couple hundred here."
Earlier in the day, Franken described the race as "too close to call" and gave no indication that he would back down from a recount. Watch Franken demand a recount »
"There is reason to believe that the recount could change the vote tally significantly," he said. "Our office and the Obama campaign have received reports of irregularities at various precincts around the state.
"For instance, some polling places in Minneapolis ran out of registration materials," Franken said. He said his staff members have been examining those issues.
Aiken said the Web site numbers are unofficial until canvassing boards in each of the state's 87 counties certify their results.
The state canvassing board will meet November 18 to determine whether Coleman's narrow victory requires a recount.
If the board decides on a recount, it would start the next day. The ballots would be hand-counted in the process, which Aiken thinks could take a week, if not two.
Meanwhile, the two major candidates in Georgia's hotly contested Senate race both said Wednesday that they are launching runoff campaigns as votes continued to be counted and neither man held a majority.
At midday Wednesday, Republican incumbent Saxby Chambliss led Democratic challenger Jim Martin, with Chambliss having 1,838,891 votes, or 49.9 percent, to Martin's 1,721,087, or 46.7 percent. Libertarian candidate Allen Buckley was credited with 3.4 percent of the vote.
"We're in a runoff," Martin said. "This race has just begun."
Chambliss also declared, "we've already hit the ground. We're getting ready for the runoff."
A spokesman for the Georgia secretary of state's office said it will probably be next week before election results are finalized and certified statewide. A runoff would be held in December.
In Alaska, incumbent Republican Sen. Ted Stevens was in a tight race against Democrat Mark Begich.
Stevens was convicted of seven federal corruption charges in October for filing false statements on Senate ethics forms.
In North Carolina, first-term incumbent Republican Sen. Elizabeth Dole lost to Democratic state Sen. Kay Hagan. Watch Hagan have the last word to her critics »
Dole, a first-term incumbent, had been considered a safe seat for Republicans early in the election cycle, but she was targeted heavily by national Democratic Party ads.
CNN's Joe Sterling and Ted Barrett contributed to this report.