Pat Toomey, a former Republican congressman, defeated Representative Joe Sestak, a Democrat, on Tuesday in a razor-thin Senate race in Pennsylvania that was not called for hours after polls closed.With almost all of the votes in, Mr. Toomey, a conservative who is also the former president of the anti-tax Club for Growth, had 51 percent of the vote, providing the capstone to what turned out to be a very successful midterm election for Republicans in Pennsylvania. Mr. Toomey will succeed Senator Arlen Specter, a former Republican who switched parties in 2009, only to be defeated by Mr. Sestak in a Democratic primary this year.

With Democrats holding a registration edge of more than 1 million in Pennsylvania, Mr. Toomey tried to appeal to independents and even disaffected Democrats during the race. But he also was not shy in campaigning against Democratic policies like the health care overhaul and the stimulus package.

“We should end the threats of excessive regulations and government overreach. We should get spending under control and put our government on a sustainable fiscal path,” Mr. Toomey said his campaign’s election night get-together in Allentown, Pa., according to a transcript provided by his campaign.

The former congressman added: “It is important to note that tonight’s victory was not a partisan victory. I could not have won with only Republican votes. It was because of Republicans and Democrats and independents that we are celebrating here tonight.”