Democrat Mark Critz smiles in Johnstown Tuesday as he greets supporters before giving his victory speech after winning the special election for the remainder of the congressional term of the late John Murtha.

PHILADELPHIA — The late Rep. John Murtha's seat will stay in Democratic hands after one of his top aides won a special election that dealt an early blow to Republicans hoping to make gains in the U.S. House in this fall's midterm election.

Mark Critz turned aside a strong challenge from Tim Burns, a Republican businessman, in a race scrutinized nationally for its potential implications come November. The GOP had hoped to capture the seat Murtha held for more than three decades by playing off growing opposition to congressional Democrats, tea party-driven discontent and unhappiness with President Barack Obama's health care law.

Critz, Murtha's district director, played up his ties to his old boss while fending off GOP criticism that he was a career bureaucrat who would blindly follow House Speaker Nancy Pelosi and liberal Democrats in Congress.

"The voters of this district won a great victory tonight. But it's ... bittersweet," Critz said in remarks prepared to address his supporters at a Johnstown victory party, "because we wouldn't be here right now if Jack Murtha hadn't left us too soon."

He stressed in the campaign that he was "pro-life, pro-gun" and determined to help a region hard-hit by job losses — Pennsylvania's statewide unemployment rate is 9 percent — policy positions that mirrored Murtha's. Democrats had a 2-to-1 edge over Republicans in voter registration in the socially conservative district.

"I think the Critz election is a powerful national message," Democratic Gov. Ed Rendell said in a phone interview early this morning. "If the theory is that the Republicans will sweep back the House, well, they have to win back seats like this and they got beat and they got beat badly."

Murtha, who was the powerful chairman of the House Appropriations defense subcommittee, died in February at age 77 of complications from gallbladder surgery.

Critz had 52 percent of the vote compared with 45 percent for Burns with 99 percent of precincts reporting.

Burns spokesman Kent Gates said the GOP nominee hoped he had "raised the conversation of fixing the problems in Washington, including health care reform and out-of-control spending."

The race was considered so close and so important that Democrats called on former President Bill Clinton to campaign for Critz, while Republicans turned to U.S. Sen. Scott Brown of Massachusetts to boost Burns.