That's quite an accomplishment in what is seen as a Republican year, but to win, Sestak needs Democratic supporters to participate Tuesday, especially in Philadelphia, taking advantage of the party's statewide registration edge of 1.1 million voters.
All year, polls in the state and nationally have shown that Republicans are more intent on voting - to send a message of dissatisfaction with Washington.
Don't write off Democrats, Gov. Rendell said Sunday.
"Democrats are much more fired up in the last two weeks than people would think," he said on CBS's Face the Nation. "I think there are going to be some surprises . . . particularly in Pennsylvania."
Republicans are optimistic about Toomey because, they note, Sestak has not been able to surge into a steady lead after catching up in the polls.
"It's going to be a close election, but Sestak has not shown an ability to close the deal," said Mark D. Harris, Toomey's campaign manager.
Sestak's forces are confident in their ground game - thousands of volunteers along with the Democratic Party and unions - and believe pollsters have been overestimating the Republican tilt of Tuesday's likely voters.
The Senate race has presented a relatively clear ideological choice between a Democrat occupying his party's left flank and a conservative Republican leader.
Sestak, a former Navy admiral and second-term member of the U.S. House from Delaware County, has been a loyal ally of President Obama, backing the financial-system bailouts begun under President George W. Bush, the federal stimulus package, and the overhaul of the health-care insurance system.
Toomey, who began his career as a Wall Street investment banker and later helped start a family chain of sports bars, is a staunch conservative who represented a Lehigh Valley district in the House from 1999 to 2005. After that, Toomey was head of the Club for Growth, a Wall Street-backed free-market advocacy group that campaigns for lower taxes and less regulation on business.
Toomey pushed five-term incumbent Sen. Arlen Specter to leave the GOP in April 2009 after Toomey launched a challenge from the right for the party's nomination and polls showed that Republicans were infuriated with Specter for providing crucial support to the Obama stimulus plan.
In 2004, Toomey came within 17,000 votes out of more than one million cast of beating Specter in the primary.
The White House welcomed Specter's conversion, and the Democratic leadership at all levels rallied around him. Sestak, however, refused to drop his plans to run for the Senate nomination, and he surged in the final weeks to beat Specter comfortably in the May 18 primary.
Since then, Toomey has led most of the way, but last month, Sestak began to move in the polls and closed in as his campaign made issues of Toomey's support for free trade - particularly with China - which many Democrats believe cost American jobs. Sestak also attacked Toomey for advocating drastic cuts in corporate taxes and backing a plan to allow younger workers, if they chose, to invest part of their Social Security taxes in the stock market.
Democrats also stepped up efforts to tie Toomey to the tea party, noting that he was a leader as head of the Club for Growth in financing primary challenges to moderate Republicans in the interests of purifying the party. Former Republican Majority Leader Dick Armey called Toomey one of the forefathers of the tea party.
The case was aided, analysts believe, when tea party-backed Christine O'Donnell won the GOP Senate nomination in Delaware, defeating Rep. Mike Castle, on Sept. 14.
"In the state's eastern media market, all the discussion about Christine O'Donnell scared Democrats into thinking they have to vote," said Lara M. Brown, political scientist at Villanova University. "It wasn't because of any particular love for the Democratic Congress that Joe [Sestak] closed; it was more because they were scared of O'Donnell. Pennsylvanians are mostly pragmatic and nonideological."
Tea party candidates, who are the GOP nominees in a half-dozen Senate races around the nation, are, like O'Donnell, mostly conservative strict constructionists. Some have questioned the constitutionality of unemployment benefits and Social Security.
Toomey, who has run a tightly scripted and disciplined campaign, has resisted the association, though he has praised the tea party.
For instance, he has refused to answer questions about whether he believes tea party favorite Sarah Palin is qualified to be president, first raised in an Oct. 22 debate with Sestak after Palin endorsed Toomey. Eventually, the media tired of asking.
Toomey has had the edge on television, benefiting from about $22 million worth of ads bought by his campaign, the National Republican Senatorial Committee, and a host of interest groups that lean to the right, including the U.S. Chamber of Commerce, the Club for Growth, Crossroads GPS, and the National Federation of Independent Business.
All told, $16 million has been spent on TV ads benefiting Sestak, $9.5 million of it from the Democratic Senatorial Campaign Committee and the rest from his own campaign.
But Sestak has also benefited from less obvious millions spent by organized labor to turn out voters for the Democratic ticket.
Democratic Party operatives, including Organizing for America and the state and county party committees, are working furiously to motivate their core voters, especially targeting Democrats who are sporadic voters or those who cast their first ballots in 2008 for Obama.
In the end, though, all of the activity may not matter if voters continue to nationalize the Senate race, viewing it as a referendum on the administration and the Democratic Congress.
In last week's Franklin and Marshall College Poll, for instance, 62 percent of those supporting Toomey said their motivation was to oppose Obama.
"I'm unconvinced the Democrats can do much at this point," pollster G. Terry Madonna said.
Contact staff writer Thomas Fitzgerald at 215-854-2718 or email@example.com.