State Sen. Katherine Clark took a big step closer to winning a seat in Congress, claiming the Democratic nomination in Massachusetts' 5th district special election Tuesday.

With 83 percent of the vote counted, the Associated Press called Clark the winner over six other candidates. She was pulling 30 percent of the vote.

The 5th district seat was vacated earlier this year by Ed Markey, a longtime liberal congressman who is now a senator. The district leans heavily Democratic: President Obama won 65 percent of the vote there in 2012.

Clark will be a substantial favorite to defeat Frank Addivinola in the Dec. 10 special general election. Addivinola won a three-way race for the GOP nomination.