Many political handicappers viewed the race as a bellwether for the mood of the electorate and a preview of how the midterm elections could go this fall.
If Republicans are to win control of the House in November, they need to secure the southwestern Pennsylvania seat once held by Murtha, who died unexpectedly in February.
They get one more shot.
Despite Critz's victory Tuesday, Republicans will challenge him again in November when the entire House is at stake.
Burns called Critz around 10:15 p.m. to concede.
Both national parties spent heavily in the race. And big-name political leaders from both parties stopped by in the last few days to campaign for their candidate. Former Alaska Governor Sarah Palin and House Minority Leader John Boehner, R-Ohio, stumped for Burns. Former President Clinton and Sen. Bob Casey (D-Pa., joined Critz on the trail.
Democrats carried a 2-to-1 registration advantage in the once-union stronghold district. But Sen. John McCain, R-Ariz., carried the region in his 2008 bid for president. Sen. John Kerry, D-Mass., won the district in the 2004 presidential contest. It was the only district to flip from Democratic to Republican in the 2008 election.
Murtha himself was elected in a special election in 1974. Many viewed his election as a harbinger of things to come in the fall as President Nixon was embroiled in Watergate. Nixon resigned in August and House Democrats went on to win more than 40 seats that fall.
Critz is expected to come to Washington later this week to be sworn-in to office. In fact, the person who will swear him in is House Speaker Nancy Pelosi, D-Calif. Murtha was a Pelosi acolyte and one of her most-loyal supporters in the House.
That said, Burns made the race about Pelosi and often featured her in his TV commercials. If "Nancy Pelosi's values are your values, then Mark Critz is your candidate," Burns said in a TV ad.
Still, Critz won't be a rubber stamp for the House Democratic leadership. Critz describes himself as an abortion opponent and is an ardent supporter of the Second Amendment. He also said he'd vote against the controversial climate change bill the House approved last June.
Climate and energy issues are critical to southwestern Pennsylvania, which features two of the biggest coal mines in the world. Democrats have now won 11 consecutive special elections in a row, dating back to May, 2008.