Iraq War veteran Seth MoultonSeth MoultonPortland: The Pentagon should step up or pipe down House panel votes to constrain Afghan drawdown, ask for assessment on 'incentives' to attack US troops Overnight Defense: House panel votes to ban Confederate flag on all Pentagon property | DOD report says Russia working to speed US withdrawal from Afghanistan | 'Gang of Eight' to get briefing on bounties Thursday MORE (D) defeated openly gay Republican Richard Tisei (R-Mass.) in a closely watched Massachusetts House race.

Tisei was one of two gay GOP candidates contesting House races this election year.

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A former Marine, 36-year-old Moulton defeated nine-term incumbent Rep. John Tierney in the Democratic primary.

Moulton thanked his supporters Tuesday night.

"From the example set by the greatest generation, to answer the call during World War II and continue to serve after they came home. America's newest generation shows renewed and growing commitment to public service," he said in a speech. 

"It is not about what's right for the Democratic Party, or what's right for the Republican Party, it's about what's right for America," he added. 

Tisei conceeded quickly after the race was called.

“Seth has served his country very admirably and very honorably in the military and I’m sure he’s going to do the same as the next Congressman from this district,” Tisei said in a speech Tuesday, according to The Boston Globe. 

This story was updated at 10:18 p.m.