DENVER – Sen. Michael Bennet declared victory Wednesday in his tight race against tea party Republican Ken Buck, suggesting that Democrats may be able to hold onto a Senate seat once viewed a prime opportunity for the GOP to make gains.

“This is definitely a race for the record books,” Bennet said in a victory speech outside the Denver museum where President Barack Obama last year signed the stimulus bill into law.

Bennet urged sharply divided Colorado voters and politicians to “set aside our petty differences and make sure this state and this country lead in the 21st century.” And he congratulated Buck, saying, “I honor his commitment to public service.”

Bennet was clinging to a narrow lead over Buck. With 97 percent of the projected vote counted, Bennet was leading by about 15,400 votes out of 1.4 million cast.

Buck didn’t immediately concede.

“We are still looking where returns need to be reported, as well as provisional ballots before making any decisions,” Buck said in a post on his Facebook page. His campaign said Buck planned to issue another statement later Wednesday.

Bennet, 45, was appointed to the seat last year to replace Ken Salazar, who became Interior Secretary. Before his appointment, Bennet was superintendent of Denver Public Schools and had never run for public office.

Democrats retained control of the Senate on Tuesday, though they lost at least six seats to the GOP. It was also unclear the winners of Senate races in Alaska and Washington state.

During the Colorado campaign, Bennet painted Buck as too conservative, especially on social issues. Buck opposes abortion rights, even in cases of rape and incest, and considers sexual orientation a choice.

Bennet and the Democrats pounded Buck with attack ads calling him “too extreme for Colorado.”

The race attracted more out-of-state campaign money than any other Senate contest this year.