By Daniel Wallis and Keith Coffman
DENVER (Reuters) - A young Republican congressman, Cory Gardner, defeated a Democratic incumbent in Colorado's U.S. Senate race on Tuesday, three TV networks projected, handing Republicans a big win in a purple battleground state.
Mark Udall's re-election had looked fairly safe until February, when Gardner, 40, announced he was leaving a safe seat in the U.S. House of Representatives to take on the first-term senator.
With 76 percent of precincts reporting, Gardner was well ahead with 50.8 percent of ballots to Udall's 43.8 percent, according to the state's flagship newspaper, The Denver Post. Fox, NBC and CBS called the race for Gardner.
At Republican campaign headquarters in a suburban Denver hotel, a jubilant crowd cheered results as a live band played. At one point, fire marshals asked some of the revelers to leave, saying the room was too packed.
Democrats said their Republican rivals made Colorado "Ground Zero" in their battle for the U.S. Senate, and 64-year-old Udall was seen as vulnerable because of his support for the Affordable Care Act, which was highly unpopular in the state.
The son of a tractor salesman from a conservative eastern Colorado farming district, Gardner won the endorsement last month of The Denver Post.
Udall, whose father once sought the Democratic presidential nomination and whose cousin is a Democratic senator from New Mexico, had followed a successful past strategy of Colorado Democrats by putting women's issues front and center.
But his bid to paint Gardner as an extremist on abortion looked to have backfired, with the Post calling it an "obnoxious one-issue campaign" that insulted voters.
Meanwhile, Governor John Hickenlooper, an ebullient former Denver mayor and brew-pub magnate who has been spoken of as a possible Democratic vice presidential candidate in 2016, is fighting to bat back a strong challenge from former Republican U.S. Representative Bob Beauprez, 66.
That race was on a knife-edge: with 74 percent of precincts reporting, Beauprez had a narrow lead with 48.4 percent of votes to Hickenlooper's 47.3 percent.
Hickenlooper, who is running for a second term on Colorado's strong economic performance under his watch, has faced controversies over a proposed school reform tax increase and stricter gun laws introduced after a movie theater shooting in a Denver suburb and the Sandy Hook school shooting in Connecticut.
Beauprez, who lost a governor's race eight years ago, has also criticized Hickenlooper's backing for a renewable energy mandate, as well as a failed $950 million tax hike for education reform proposed by the state's Democratic-led legislature.
(Additional reporting by Rick Wilking in Denver, and Anna Yukhananov and Susan Cornwell in Washington; Editing by Doina Chiacu and Eric Walsh)