Former Republican state treasurer Bruce Poliquin has established a lead over Democratic state Sen. Emily Cain in the race for an open seat in the 2nd Congressional District.

Poliquin has a 10-point lead over Cain, while independent Blaine Richardson is a distant third, according to a Portland Press Herald/Maine Sunday Telegram poll conducted by the University of New Hampshire Survey Center.

Among likely voters, Poliquin garnered 40 percent support, Cain had 30 percent and Richardson had 3 percent. All three candidates received additional support when interviewers asked voters whom they were leaning toward, but the margins between the candidates did not change.

The congressional survey, part of a larger statewide poll, has a 6.2 percent margin of error because of the smaller sample size. The survey of 220 likely voters on landlines and cellphones was conducted from Sept. 18 to Sept. 25.

Nonetheless, the results are positive for Poliquin, who is trying to become the first Republican elected to the seat since Olympia Snowe held it from 1979 to 1995. Democratic U.S. Rep. Mike Michaud, now running for governor, has won the seat six times.

The prospect of an open seat has attracted outside groups to the race. U.S. House Speaker John Boehner was in Portland on Thursday to raise money for Poliquin. The Democratic House Majority PAC, a super political action committee, purchased $268,000 in television ads to support Cain on the same day.

According to an analysis by the UNH Survey Center, Cain is relatively unknown but is liked among those who know her. Thirty percent said they have a favorable opinion of Cain, 18 percent have an unfavorable opinion of her, 8 percent are neutral and 43 percent don’t know enough about her to say. Cain’s net favorability rating is +12 percent, down from 15 percent in June.

Poliquin is also relatively unknown in the 2nd District, but 35 percent have a favorable opinion of him. Twenty-two percent have an unfavorable opinion of him, 8 percent are neutral and 35 percent don’t know enough about him to say. Poliquin’s net favorability rating is +13 percent, an increase of 3 percent from June.

Richardson is also largely unknown. Eighty-six percent said they didn’t know enough about him to have an opinion of him.

The 2nd District race is the most competitive of Maine’s three congressional contests.

In the U.S. Senate race, Republican U.S. Sen. Susan Collins leads Democratic challenger Shenna Bellows, 59 percent to 29 percent with 11 percent undecided among poll respondents. The Senate race had a larger sample size and 4.4 percent margin of error.

In the 1st District, Democratic U.S. Rep. Chellie Pingree has a commanding lead over Republican Isaac Misiuk, 66 percent to 13 percent. Seventeen percent are undecided. Independent Richard Murphy was an option in the survey but did not receive any support, and only 2 percent of participants knew he was running.