Musgrave, who has represented Colorado's 4th Congressional District since she was elected in 2002, has had tough re-election fights ever since, The Denver Post reported Wednesday. The seat has been in Republican hands since 1972.
Markey, a small business owner, ran as a moderate in a race that was dominated by negative campaigning, the newspaper said.
With 67 percent of precincts reporting, Markey was ahead of Musgrave by 57 percent to 42 percent.
2014: The Year in Music [PHOTOS]