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The nation's most anticipated U.S. Senate matchup became official last night as Democratic Treasurer Bob Casey shrugged off the opposition of two liberal rivals to claim the spot on the November ballot opposite U.S. Sen. Rick Santorum.

"This is, in many respects, the national election of the 2006 cycle,'' Mr. Santorum said, heralding the national focus on the contest as he celebrated his nomination in his Green Tree headquarters.

The two-term Republican incumbent had no opposition yesterday. Gov. Ed Rendell and his general election opponent, Republican Lynn Swann, were also unchallenged for their respective nominations for governor.

In early tallies, Mr. Casey had collected more than 80 percent of the Democratic votes while his rivals, Alan Sandals and Chuck Pennacchio, were stuck in single digits.

Despite the energetic opposition of Mr. Casey's more liberal challengers, the primary had long seemed little more than a formality. For months, the Democrat has focused his campaign almost exclusively on the incumbent, characterizing him as an extremist and tying him to the policies of the national Republican administration.

Mr. Santorum has, in turn, done his best to turn the spotlight on Mr. Casey, hoping to shake up the dynamics of a contest in which his challenger has held a steady lead since he first announced a candidacy that had been courted by many of his party's state and national leaders.

Mr. Santorum renewed the effort to draw out his opponent as he accepted congratulations in his Green Tree headquarters last night. Accompanied by his wife and children, the Republican acknowledged initial odds against him but pledged to defy them.

Recalling that this was the fifth Republican nomination for Congress he'd accepted since his maiden run in 1990, he said, "Each one of those times, we were given very little chance of winning ... [but we've] come up a winner every single time, and we're going to do it again.''

Renewing challenges to Mr. Casey that he'd first issued months ago, he called for a series of 10 debates between now and November and demanded that the Democrat announce his position on every vote that comes before the Senate between now and November.

"Come out from behind the name and come out before the voters of Pennsylvania and talk about the issues important to this campaign," Mr. Santorum said to the cheers of roughly 80 partisans. "The people have a right to know what you think."

But in a statement released shortly after his electoral walkover became apparent, Mr. Casey, who watched the returns in his home in Scranton, made it clear that he would continue a strategy of casting the race as a referendum on the incumbent and the administration he has supported as the No. 3 Republican in the Senate.

"Tonight voters from across the state overwhelmingly showed President Bush, Rick Santorum and the whole 'wrong direction' gang in Washington that the values that unite us as Democrats are stronger than anything that might divide us,'' the Democrat said. "It is clear that our country needs a new direction and Pennsylvania needs a new U.S. senator."

Mr. Sandals, a Philadelphia pension lawyer, and Mr. Pennacchio, a Bucks County history professor, carried the hopes of Democrats who resented the party hierarchy's embrace of a candidate with relatively conservative views on divisive social issues such as abortion and gun control. But neither was able to make a serious dent in their party's consensus support for a candidate who two years ago, in winning his current office, set a state record for the largest vote total in Pennsylvania history.

The stakes in the general election race are reflected in its robust early fund raising. By the end of April, Mr. Santorum had raised $13.7 million, and had just over $9 million in cash, putting him near the top of Senate fund-raisers in this election cycle.

Mr. Casey had raised more than $8 million and had a balance of $4.5 million, figures that, while well behind the incumbent, made him one of the best-funded Senate challengers in this year's elections.

Mr. Sandals, by contrast, raised only about $688,000, most of it his own money, while Mr. Pennacchio raised $97,000.