Rep. Mark Critz (D-Pa.) defeated fellow Democratic Rep. Jason Altmire in their primary on Tuesday, in a major victory for unions.

The Associated Press called the race shortly after 10:30 p.m. Altmire conceded to Critz before the race was called, however, congratulating Critz on win.

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"Congratulations to my colleague Congressman Mark Critz on his hard-fought and well-deserved victory in the primary. He has my full support as his campaign moves on to the fall," Altmire said in a statement.

With 98 percent of precincts reporting, Critz had 52 percent to Altmire's 48.

The two lawmakers were thrown into the same district by Republicans who controlled the redistricting process. Pennsylvania lost a House seat due to population decline.

The new district is mostly Altmire's old territory but the three-term lawmaker incurred the wrath of unions when he voted against Democrats' signature healthcare reform bill in 2010. While Critz, who was not in Congress at the time, has said he also opposed the legislation, many union heads said Altmire had led them to believe he’d support the bill.

Altmire had led Critz in polling but both lawmakers told The Hill last week they expected a close race.

Critz, a former staffer for the late Rep. John Murtha (D-Pa.), was endorsed by former President Clinton.

He won't have an easy general election race, either. He'll face Tea Party favorite Keith Rothfus (R), who nearly beat Altmire in 2010, in a district that leans slightly Republican.