(CNN) - Montana Sen. John Tester successfully fought off a challenge from six-term Republican Rep. Denny Rehberg in a hotly contested race marked by heavy outside spending on negative advertising, CNN projects Wednesday.
Republicans considered the seat a possible pick up in their attempt to win control of the Senate.
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Tester had 49% compared to Rehburg at 45% Wednesday morning, with 83% of the vote counted.
Rehberg, the state's sole representative in the U.S. House, issued a statement Wednesday morning thanking Montanans for their support throughout his campaign.
"It has been an honor to serve the people of Montana," said Rehberg. "The voters of our state have spoken, and I respect their decision. Senator Tester and I share an abiding love for Montana and America, a value which transcends political party or disagreements on matters of policy. I congratulate Jon on his victory in this hard-fought campaign."
As of 11 a.m. E.T. Wednesday, Democrats control 52 seats in the Senate to Republicans 45 seats and two independents.
Meanwhile, Republican Steve Daines won Montana's 1st Congressional District to replace Rehburg.