U.S. Rep. Tim Murphy survived the Obama tidal wave in Pennsylvania.

Mr. Murphy, a Republican from Upper St. Clair, yesterday won his fourth term in Congress, defeating Democrat Steve O'Donnell of Monroeville.

He said he took nothing for granted and put all his effort into a winning campaign.

"We worked very hard. We never sat back," he told supporters. "Victory would not come to those who sit and watch."

Democrats hold a registration edge of about 60,000 in the 18th District, which Mr. Murphy has represented since 2003. But he once again overcame the numerical disadvantage to win with ease.

His race with Mr. O'Donnell was shrill and acrimonious. Each man accused the other of misdeeds, but Mr. Murphy had far more money to get his message out.

Mr. Murphy, 56, built a quick and solid lead in the South Hills of Allegheny County and then held it all night. He also domionated the other parts of the district -- sections of Westmoreland and Washington counties.

Mr. O'Donnell, 62, a previous contender for a state legislative post, hit Mr. Murphy hard for supporting the Bush administration on economic policies and the war in Iraq. He also made a point of telling voters that Mr. Murphy is under investigation on allegations that he used his congressional staff for campaign details.

But most of Mr. O'Donnell's campaigning was done with shoe leather. He could not afford to buy television time. Mr. Murphy could, and he used many of his ads to criticize Mr. O'Donnell.

In his commercials, Mr. Murphy suggested that Mr. O'Donnell profited personally while a social services agency he managed in the 1990s went bankrupt. Mr. O'Donnell said the agency was $500,000 in the black when he was in charge.

He complained that Mr. Murphy used "desperate and dishonest" tactics in the campaign.

But Mr. O'Donnell remained an unknown to many voters, and he could not piggyback on the success of Democratic presidential nominee Barack Obama.

In his four winning campaigns for Congress, Mr. Murphy has never faced a Democrat with a sizable bankroll. The financing trend held this time as he outspent Mr. O'Donnell by a wide margin.

Facing defeat late last night, Mr. O'Donnell had not yet spoken to his assembled supporters, who gathered in a Monroeville firehall.

As the night wore on and Mr. Murphy's lead lengthened, some of Mr. O'Donnell's backers lost their focus.

"I'm celebrating Barack Obama's victory in Pennsylvania," one said, not wanting to talk about the congressional race.

Though Mr. Murphy's win appeared easy, he said he was worried. "We were very concerned all along," he said.